Hi, can I suggest you something?
The game is perfect, except for the shooting system:
Needs a limit to consecutive shots (eg. 1 each second), becouse with rapidfire you can cover all the screen with bullets, killing the difficulty (with this new shot rate, rapidfire is welcome!).
Remove the shot sound (tedius, this is one of the first rules for the shoot'em up genre, also useful to hear enemy shots only).
Ah, a last thing... rise up the difficulty level, please!!! :)