Whoa, this is kind of amazing! I have to admit, it took me a while to figure out what even to do. I was kind of wandering back and forth, shooting stuff...then I started shooting myself upward and it was like "Oh...OHHHHH OKAY". Then it got pretty crazy, in a good way. It plays smooth, the animation is great; the white-red pixel-y graphics are pretty cool. I liked how each of the weapons felt different. The boss was pretty impressive too!
One thing that kinda bothered me is that when you die, it's not even obvious. I mean, I understand wanting to get right back to the action, that's great. However, there was this confusing moment of "What happened? Where did I go? Did I die? Do I even have health?". Just something to telegraph what happened, like a special sound, or something. Also, something kinda weird happened; I was fighting the boss, and I died (I think), and suddenly it got into this state where the boss was pushed up to the top of the screen, and I was stuck right above it. I didn't lose health, but all I could do was keep shooting, and this eventually defeated the boss. Odd.
Still though, those are minor problems for an impressive effort!