Amazing game! Graphics are minimalistic but really fitting, the gameplay is simple but because bullets interact with anything opens up to many possibilities, it is great!
Please, please make a post jam version with music, and maybe some more types of enemies. And also, I think it would make for a great mobile game, since the controls are really simple.
Only thing I have to say is what you said yourself - more content, and music. Oh, and maybe change up the sound effect for activating this shield around you?