This is superb! The graphics are adorable, I especially love the waves and the parallax background in the second stage. The powerups are great, too. The gameplay is nice; starts out simple but it does get difficult!
There were only a couple of things that bothered me. First, is there a point to crouching? Or maybe I mean, is the best strategy just to crouch ALL the time? Also, when the enemies shoot at you, their shots are usually very small and difficult to see. And finally, when you lose all your health, you just kinda go off the screen for a bit...That's fine, but personally I'd like some sort of animation to let the player know what's going on.
I think for a jam game, though, you did a pretty great job!