Very cool idea. Also the colors are pretty great most of the time. Plus everything interacts with everything, which is nice! :D
In my opinion the game goes too fast when moving or shooting. You can't dodge bullets anymore once an enemy is too close and you can only fire so fast... That makes it feel a little unfair at times and it also makes dodging the inferior strategy overall. Just standing still and firing as much as you can is the best strat most of the time. That's a small balancing issue in an otherwise great game, though. Good job!