Demo review:
You click your mouse a few times for a few seconds, get a little belly, and instantly lose at 150 points. I don't get why this demo even exists, it's too short, doesn't really showcase anything other than the intentionally-floaty controls, and honestly some screenshots would've done a better job demonstrating what the game's about. 0/5.

Full game review:
A very janky sidescrolling game where you eat fish smaller than you (they're basically all the same size and most are already smaller than you, so there's really no strategy here), and various obstacles and some powerups get in your way as sharks zip by and try to eat you. Very arcadey, but thanks to how all the mechanics work out, there's really not much skill or strategy involved, mostly luck, hoping you don't get ricocheted off something right into a shark.
Janky hitboxes, repetitive gameplay, running the same loop of content 9999 times, getting bored and trying out some of the game's challenges so you can unlock the ability to later unlock a mermaid, and so on.
What also rubs me the wrong way is that by the time you unlock any new mermaids, you've already done everything in the game. I've played 95% of the game's content and I'm still using the base mermaid, for example. Would improve the game vastly if you didn't have to wait for an ACTUAL IRL timer to unlock mermaids after you've unlocked the ability to unlock them. The game isn't nearly long or complex enough to justify it.
I could go off on a list of grievances, but I already put that in the comments section of the game.

Anyway, the game's saved by two things: the price ($3), and the art of the mermaid and the shark. Would rate the game 3 stars, but that demo being that short and simple makes me drop the rating one star out of spite.