Nice, and very fitting to the theme, but I think difficulty increase is a bit too slow for a jam game where people have limited attention-span.
Are you aware that you can reload while holding your "aim"? I mean, if you charge a shot holding the mouse, then keep it held and press R, you will reload but also be ready to instantly shoot. Not sure it was intended, as it's an interesting mechanic but does not seem to fit the theme of the action.