Data:
The game was made by Igasenpuuki ( いが扇風機 ) (styled as: igasenpuki) (blog)
The original free version can be found there, hidden under the word 'こちら'. There is also a mac version. The latest game version is 1.5. (There was no need to get it from Game Atsumaru)
Monster TS Game 3 is part of a series of games. It is a sequel to Monster TS Game 2, which is also free. A character that used to be an old man (turned into a little boy) from that game appears in this one.
Monster TS Game (free) was the first game in the series and the part commercial game TS Monster Island which was freely playable on Game Atsumaru seems to be the last game. This last game has a demo you can download and play for free.

Up front:
I would age rate it 18+. It seems to be a fetish game. It's a bit disturbing too, due to the nature of the content.

To me, it seems it is trying to appeal to power fantasies like omnipotence, extreme beauty, 'being a source of erotic excitement in the eyes of others', 'making others jealous about what you are'. Although with every transformation, except for two of them, the protagonist also suffers identity death (loss of memories, replaced personality, replaced feelings, inserted knowledge / memories / ideas, loss of original desires, will, interests etc.), just to fit the role that is associated with the transformation. In all cases either they themselves become the source of the power fantasy or whoever dominates them is. Every time identity loss / death happens the character thinks they are female, yet they keep having the male gaze. In other words, they admire how they look 'because it makes other men gaze lustfully at their chest' (for example). This is not how a woman normally thinks of their own body. The protagonist often ends up feeling like some kind of diety or god, or becomes a high in position and just serves that role of power, or simply becomes extremely cute or beautiful even to the point they can't even handle their own reflection. For example: Queen of the Forest, Vampire Princess, Succubus Ruler, Queen of the Harpies, Demon Princess. Even the alruine ending is about being in control, being pretty. You may argue, slave elf, but again, look at how the elf is described; it's extreme beauty. Same deal, just not with position, but with being prettier than everyone else. The only exception is one specific ending with fairy, but that one is immortal and also up front its announced that fairies are worth 1,5million gold, which no one except a king can affort, so there is still some "I'm better" in there.

If you have narcissistic desires, then this game may appeal to you as such.

Most transformations have at least two endings. Other transformations I haven't yet mentioned are bunny girl and dog girl. Both of these have three different endings. One other ending is the not-transformed ending.

Each transformation is associated with a specific quest and unique areas where, other than sometimes being able to travel there isn't much to do unfortunately. That said, the fox endings require a simple puzzle and both the fairy and the alruine ending require investigating in a specific order to avoid (which likely you don't want to by the way). The harpy ending has a stealth event (sneaking behind lines of sight.

The areas in game are 'town', 'slavery sale's section', 'casino', 'quest hall/library', 'hotel', 'item shop', 'church' (to cure transformations), and the quest specific areas. There are also cutscene specific areas, but you can't play there at all so... no clue. The game takes about 5 minutes to clear from start to true ending. To a bad end it takes 2 minutes. (Though bad ends are actually good endings for the protagonist, except that they are transformed.)

The disturbing parts:
All of the art is moé based. Eyes are big, etc. Eyes are especially big for child characters. The thing is, this makes them look younger and makes the game appear as if it's for younger audience. It's not.
I also do need to note that it seems the protagonist and their victims are not allowed to be themselves (identity death). The protagonist who is an experienced adventurer (somewhere in his 20s).

One of the quests takes you to an abandoned house where there is a pervert who is into young girls, as in, middleschooler or younger. This character transforms the protagonist in an angel-loli (as it is described), a cute little girl wearing a white lolita dress with decorative wings (that according to the in game lore, looks less than 10 human years old). You can argue that the protagonist is still somewhere in between 20 and 30 of age, but as I mentioned it seems every transformation is affecting the protagonist mentally and sometimes their 'soul' even according to the lore. The protagonist also gains sudden skills, but anyway... once the protagonist loses the battle, this pervert character actively uses the protagonist new found innocence and weakness to force (former him) 'her' onto a bed and starts engaging in his ... desires. I am not sure what activity specifically, because the author then comments "skipping scene because this is only for 'concenting adults'". Keep in mind the original language is Japanese, which is often used in a very indirect and suggestive manner generally. In indirect communication, you're expected to 'imagine' what someone maybe meaning besides what they are saying to get what they intend or want, so-- it doesn't help with this scene. The entire suggestion, to me and to most people I assume, means the game contains actual child sexual abuse and rewards the pervert who goes unpunished to complete satisfaction. Even what is actually shown, a creepy man forcefully dragging a little girl onto a bed would be traumatizing for a girl if that were to happen in real life, and is as such abusive. We can also see a scene later that the protagonist has been completely mentally converted into this pervert's perfect 'little sister', where he tries to make her as cute as possible. In another variant of this ending, the pervert also gets transformed into the same girl, essentially becoming her twin, and announces he can then do to other girls of that age whatever he wants (including some specific sexual acts) and get away with it due to his (now her) new found age. (again rewarding the child sexual abuser + announcing more abuse will follow in the future in that fictional universe).

And that is not the only time child-abuse happens.
In the demon ending, the 'mother' removes the thoughts and memories (along with their feelings as such) of the child (6 world years old) or starts gaslighting her in order to convince her that her former reality never happened in order to keep her in control and turn her into the perfect daughter.
In the vampire ending, the younger sister gets kidnapped and locked up in a cage, because she can be turned into profit.

There is also a rape ending and yes I recognize it is fiction and just a game.

Opinion on the game:
It's unfortunate, but the game is actually kinda bad. I'll explain why.

I'm a bit disappointed on the lack of any sort of challenge. It's extremely minimal. The fairy transformation had a challenge that is worth noting though. The most lengthy thing in this game, what got spend most attention on is the writing, so I think that deserves the most attention for scoring, and unfortunately this too is kinda bad. That said, the art looks okay, nice even. It's just the combination of the art + setting in some endings that make it disturbing, but generally the art that they added or made themselves is nice.

So I'll focus on the story, lore and flow of things for the opinion.

Before I played this game I played TS Monster Island. Someone provided me with a robot translation of the texts which was enough to play it. That game is seemingly, basically the same as this one in its setting, what you can do and the way things work. So what i first noticed is that the exact same ideas were reused as such; some assets were also reused. The two games are similar enough that you may confuse them as such, but they are still separate games. In the omake room, which you can reach after obtaining all endings, you even see cut ideas mentioned that are present in TS Monster Island. I highly suspect that the author of the game did the same with Monster TS Game 2 and this one. I see very little completely different content due to this. Although similar, the endings at least are different. For example in TS Monster Island, succubi are also an infection / virus, spreading quickly and you're supposed to help slay all succubi. It is because of that you end up being either turned into a child succubi or adult one, but in this game you have that same idea, except that it is you does the spreading of the virus here and, seemingly to satisfy the power fantasy, no one dares to oppose you since you're too strong and it is too dangerous. There is a vampire and practically exactly the same, vampire sister ending there as well. You also have a fox girl ending with godly powers. You get the point I think.

A second reason is because most of the writing is spend on the fetish parts (power / beauty fantasies) of the game. NPC's thoughts are like "Oh my god, she is so hot (or cute)" The protagonist starts playing with their new body upon transforming every time (with two exceptions). If you hunt down all of the endings, you'll because of this read the same stuff over and over. With each transformation the same things happen, just with some different details or different words. It's basically, "Oh sensitive", but then with a lot more text. And yes, it includes the descriptions the power fantasy aspects. "Cute, very cute.", "most beautiful...", "My abilities make me feel amazing...", etc. There practically isn't any time spend in 'dealing with the transformation' at all. They tend to skip over this with deus ex identity alterations / death or deus ex sudden knowledge; and when turning back to normal too, it is a mere flash that has nothing to reflect upon, except the caster saying "that was unfortunate." or "oh well". Like.. sigh-

What I, and I assume monstergirl fans would like to see, is the protagonist struggling and dealing with the transformation and its consequences instead of having a deus ex cheat allowing them to instantly deal with it as if it was always that way, or a cheat mode exit.  Every transformation ending is in all cases beneficial to the protagonist (satisfying some kind of power fantasy). Thenks to their identity death, they either don't need to deal with it at all or they get help (despite their deus ex talents for it), so we never get to see anything on learning to deal with their new form. The one exception is of the vampire sister endings, which is still very minimal. Things like learning how to fly, learning magic, learning how to pose femininely, etc. seems to get skipped over or magically filled in. Deus ex benefits only. Even in the elf slave ending, the protagonist's captor will almost certainly die before them and so the protagonist remain beautiful, etc. With the other vampire sister ending 'lets give them instinctive instructions', fox ending too 'Deus Ex Machina', now protagonist knows god-skills, has no issues with their form and all auto knowledge on how to do stuff. It's absolutely lazy and terrible. The reason why Monster Musume no Iro Nichijou is popular is not just because of it containing monster girls, it's because each character has their own personality, each character has their own problems, each character grows. The show, manga, whatever, shows problems, having to live with them, etc. The only transformation where in part it becomes a problem for the protagonist is when they are turned into a fairy. And this isn't even because of the transformation, but instead because they are locked up, because of the setting as such. There is still a lot of deus ex machina going on; magical flying skill, suddenly knowing magic (a scene later)

In other words, the transformations in this game feel pointless and could have been any transformation or even no transformation. Anything could fill that role. The same scenes wouldn't miss the transformations. This is very unfortunate and so, it to me seems that these transformations, the monster girls, they're just there for fetish fantasy reasons. (Because they are pretty, powerful and not seen as human, but as something more and are desired.)

Personally I don't like power fantasies or anything that clearly tries to put other characters and people below them, even if it is just shoving everything in the same category or some other simplification, etc.

Another thing worth to note here is that the author made a 'ts game', so we expect a focus on the male to female transformation aspects within the game itself or its consequences; but the entire theme is skipped over using identity death and deus ex knowledge/skills. It's also skipped over when the protagonist transforms back and their memory of the event is wiped. In fact, the entire game, any quest you do and clear, it never happened. Reality resets as if you press new game with just one NPC (the loan shark) not acting like this. It's always the same day, the NPCs are practically frozen, the quests never completed, etc. You can redo the same quest over and over due to this, but as such the transformation involved wiill be the first time for the protagonist every time. And the priest, also sees the protagonist transformed for the first time when they heal him, even if it is the 5th time. None of the actions the protagonist makes matter, not even while transformed, so the transformations do not matter for a number of reasons. Because they are convinced they were always a woman and no one else notices anything, you may as well not have a transformed protagonist. It's terrible writing in my opinion.

To conclude I think this game's intend is to appeal to sexual fantasies and power fantasies mainly. It's a bit lacking on the transformation content, strangely enough even on the genderbending despite being called a TS(F) game. Being transformed is not much of a deal for the protagonist, except for that short moment while they lose their personality. (except during fairy and dog transformations). The only comments the NPCs give you are "Owh boobs". (They're unaware of the transformation, much like the protagonist). The protagonist also keeps their male gaze aspects, so they only think they are female, they pretty much think like males and so don't mind being sexualized on their feminine aspects (they even want that to happen) and they do it to themselves and others as well. Although the game doesn't admit to the protagonist keeping the male mindset (and pretends woman think like that). It's also unfortunate, because the game could be playing in on that as well. (By that I mean the protagonist being unaware of how male they are thinking; but in the game's lore even the succubi think that way). The consequences of the protagonist's identity death while being in a transformed state means it has always been like that for the them, it is their original normal, and so it breaks the whole TS part of the game. Even if the protagonist appears to be weak, innocent or afraid, that is just an alteration made to their personality that is there to make them automatically more appealing, childish or cute. (It's a tool so that the protagonist doesn't need to learn how to act or be cute, a skip for the author) In other words, the protagonist will not ever ask how to wear 'insert any female clothes', or visits the bathroom, etc. The TS / transformation content maybe there, but at a bare minimum, so much so that it may as well not be.

The best transformed ending in my opinion is the Dog Ending, where the protagonist is still themselves even with a new body. They have to learn how to deal with things, etc. Yet all of that unfortunately happens off camera with a years long timeskip. It's also in my opinion the most wholesome despite appearances; this is because in the other endings there is always some catch that, despite it looking cute, is actually terribly dark and gaslighting. The dog transformation is also one of the two transformations where the protagonist doesn't immediately start to fap with their body.

The canon non-transformed ending is extremely short and way too normal, especially compared to the transformed endings where there is a centric focus on how powerful the protagonist suddenly is, as a monster or due to their position. The areas are designed interestingly at least. The game itself is short and setting wise feels more like a mesh of reasons for the protagonist to become prettier or more powerful as a monstergirl. Any previous actions done are undone even after obtaining the reward for it (which makes no sense). The only exception as mentioned before is the loan shark. If you pick quest 2 4 times (kill the succubus), you can leave. If you do that, you clear the game in its intended ending, which can be done in 5 minutes or so. Its small.

But anyway those are my thoughts. I also think this game would be illegal where I live due to the angel-loli endings. Not sure what score to give this.

Opinion on the translation:
It as others mentioned, it is likely a robot translation. There are also some issues with the translation, such as a line in the Succubus Ruler ending has its color scheme broken and a number of things such as the "Load game" option remain untranslated. The game is despite this playable and, I am not sure of this, but I do think the translator took the time to try and insert personality quirks. It's possible that the original author did add these 'thought lines' though. I think the translation could use a second look.

Good game!  It's a complete experience.  You basically go around and take 1 of several independent quests that each lead to a different transformation path.  The transformation paths each have different endings, all of which are catalogued in a sort of "ending library" where you can review any ending that you've achieved as well as get hints to the remaining ones.  As someone who has completed every ending in this game, my advice is to save often.  Paths can diverge pretty early on, and you might miss one entirely if you're not careful.  But the in-game hints make it pretty easy to figure out once you know where to look. 

Things I like:

• Full art!  Each transformation has art, and many have intermediate art of the steps leading up the the final transformation.
• Detail!  Even in the "bad ending" transformations, the character gets a short chapter for almost every one where they get to walk around town post-transformation and interact with the villagers.  Some of these scenes are really good.  Every transformation gets a fair and more or less equal amount of content.
• Quick!  The pacing is fast and the pattern of gameplay is easy to figure out.  This "game" is really more of a catalog of short transformations, and I enjoyed it a lot.

Things I didn't:

• The dialog was a little rough at times, it feels like it was translated by a Japanese speaker/machine and not an English speaker.  While you clearly get the message in pretty much every case, it gives this dialog a sort of uncanny and goofy feel at times where it definitely wasn't supposed to be that way.
• Unoptimized!  The game *technically* can run on my macintosh laptop, but man did it get hot and scream at me the whole time.  Additionally, during the succubus quest, the game runs at ~1 FPS when a particle effect is supposed to trigger, at which point I just kind had to leave the game running and pray that it recovered.

Short, but fun game! Love that the art CG is actually consistent! Cute TFs stuff from loli angels to busty harpies where you can even control them for a time instead of straght to a bad end. Would reccomend for monster girl TG fans. 

Overall a good translation - however - the first lost End game is .... well a little girl (the words of the game) that is "raped" by an old prevert! This is really not a good look for a game to have child molesting in it, even if "animated".

Could I suggest that the Little Girl is changed to something different? For example, a Young Woman, or something like that. I mean "rape" is bad enough, but having it identify the character as a little girl was.... um.... shocking!

A decent short-ish game. The writing and occasional puzzles/sneak minigames are not terrible, but nothing to write home about - the real attraction is actually pretty good art. Quite a lot of art, honestly. NSFW content is completely censored, although things are more or less directly stated to happen at least in a few endings.