I've just finished the game and thought it was really fun! The level of challenge ramps up well, going from easy to just hard enough on the final level. The hats add a nice bit of variety. I encountered no bugs in the gameplay or lag, other than one of the ostriches suddenly growing a 300 ft neck at one point.
However, one thing that may need fixing is that if you beat a level with 3 ostriches and then play again and save 4 ostriches, the level select counter doesn't update. That means you need to wipe your save file and start again if you want a perfect score. It's worth playing again though!