Overall a very enjoyable cyoa game, with just a few minor typos. 

However, like pretty much all games by Lily, it's rather short.

This is a fun little CYOA-style game about multi-boobed naturally polyamourous lesbian mermaids frequently having sex. They also practice a sport that consists mostly of making out, and get each other pregnant occasionally. Also, mermaids are apparently bought and sold by humans as livestock/slaves and cost a lot of money, but don't seem to mind too much and are trusted enough to go swimming in the sea and come back. Oh, and some of them can use magic. The setting doesn't make a huge amount of sense - but it does facilitate a lot of well-written mermaid sex scenes, so I'm not complaining!

Don't expect deep characters or a complex plot; both are fairly one-dimensional, and exist primarily to facilitate the sex scenes. That's not a criticism; this game focuses on one thing and does it well.

My biggest criticism of this game is that it features numerous places where it feels like the player should have a choice, but only one option is listed. CYOA games typically consists of passages of narrative, followed by hyperlinks that lead to subsequent sectons of the story; when a passage ends with an unanswered question or unresolved plot point, it's usually followed by multiple hyperlinks that let the player choose which direction to push the story in. In Mermaid Sumo, however, some passages of that type are followed by only a single hyperlink. For example, (spoiler ahead) there's a moment in which the newly-female player character's girlfriend says she'll only try sex with the player character if the player character is willing to try having sex with a man. It's presented as a choice offered to the player character, so it feels like it's supposed to be a branch point where the player can choose between having sex with a man and giving up sex with their girlfriend - but there's only one option presented, and it wasn't one I was interested in.

Despite this, I enjoyed playing the game, and played through every path but that one.