A unique and very well-made game.
I have to congratulate you for making this excellent game. Not only is it alot of fun, the graphics are top-notch and I really like all the new weapons and items you can purchase. The greatest thing about it though is definetly the gameplay. I could tell you were trying to create a game similiar to Guitar Hero, no? If that is the case, you pretty much nailed it. Also, I like the little wink towards Resident Evil (that being Jill, of course).
Anyway, I suppose you want some constructive critisism too, so here goes:
The graphics were at some points way to intense and it became a bit laggy. Even on the lowest quality there was some delay. Also, I really would have liked the game to include more levels and harder tracks. Other than that, I can't think of anything to improve. You should make a sequel to this, no doubt.