First of all, the art & animations are great.
I could handle most things, at least until the gun comes out. It just again proves that, guns are the best weapon. I reckon that a smoother difficulty curve might be worthwhile - only spawning one obstacle per track first, then adding on to that with the enemy variety and more obstacles and speed.
Contrast is also pretty low - it was difficult to discern obstacles from the background, making it a bit harder.
A little bit of tweaking would do this game justice!