Ooo...
It's a pretty novel idea to have a shooting game where you don't control the shooting. It doesn't sound too cool, though. The inclusion of pickups was wise on your part: makes everything seem that much more hectic. Some things reminded me of Geometry Wars (in a good way), like the crazy parts where a huge wall of rocket ships would appear and scream death at you. All in all, I liked it, and I'll probably play it again. What could you improve upon? Hmm...
I dunno. For this kind of game, it seems like you really hit the nail on the head. Maybe if you included different difficulty levels. Wait, did you? Lemme check...nope, don't see any, although I do appreciate the second gameplay mode. Though, that one is over a bit quickly and seems a little too easy (despite all the death-screaming rockets). Extra difficulty modes might make certain people feel like badasses, but I don't really mind.
No, I can't really find anything for you to improve upon. I guess that means I should give you a perfect score, right? Dodging stuff with the mouse is fun for me, and it's kind of like an added bonus to see that stuff explode and drop goodies.