Zooming around and cleaning up the water is real fun, the sprites and music are good as well. The minimap and bars in the UI are also very satisfying. Getting speed and doing a jump out of the water is the best
Getting a long trail of slime behind you is almost as fun as getting a single huge ball of slime
I think I beat all the enemy fish by just holding D and they all died offscreen, a little bit of a chase or effort there would feel better
Make sure that % remaining doesn't round down to 0 when there's still stuff left
An unfortunate byproduct of how the game works is that its most fun right at the start: you go as fast as possible and get a huge thing of slime without really trying. Near the end you're going slow and double checking everything for the last stray bits of slime.
Spitballing ways to help this, pulling back the camera when you go fast could help you see slimes easier, making the slime pickup hitbox larger at speed could make it easier to grab stray single slimes, the water clearing up as the slimes are taken away could help indicate where the last ones are (and is also satisfying like powerwash)
Good work overall!