Mechanics and game-feel are top-notch. Great work here. It's a little on the difficult side (I'm very bad at shooting in pretty much any game), but I still had a lot of fun.
I think my only real complaint is that I kept thinking one of the power-ups was for a permanent health increase, but it never did anything (After I *did* find the upgrade for that, I realized that it was just a refill, and I was already at full health).
Solid game, keep up the good work! :)