Great concept, lots of bugs.
The game looks and plays great. Except for the lag. The game drags like hell once anything's actually going on.
And the controls are jerky. Sometimes, I would make a move, and then the piranhas would just bounce halfway across the screen for no reason. Often into the jaws of a shark. Speaking of sharks, every 4 seconds is a bit excessive.
And often, I would click on the upgrades button in the menu, only to have the screen get stuck with no options on it, only a picture of my fish, forcing me to refresh the browser to resume my game.
With jumping, for some reason just barely breaking the surface of the water causes you to fly the whole length of the screen in an uninterruptable slow motion that takes forever to complete.
Aside from all of these problems, the game is actually quite fun. Addictively fun. And I enjoyed playing it all the way to the finish.