My only problem is how long it takes at the beginning to finally get big enough to eat things, maybe make the percentage of small fish higher in the beginning and lower once you hit a certain score? I don't know how easy that would be.
I do however like the powerups, the music, and the scene at the end. This game is pretty addicting, even if I die when I'm big, I want to play it again to try to get all the way to the end.
The graphics are fine, it's easy to tell which fish is which, and which are powerups or just regular. If you want more detailed, cool, but I don't think this game needs it because the graphics and music fit well as is.