you could have made more of this
i really liked the idea of this but:
if you dont read every detail of the instructions you dont have any clue what the hell is going on... well ok thats not really a mistake but i find it inconveniant in this kind of game.
also you should really work on the game mechanics. the enemies are often half the size of the screen everything move really fast but the projectiles of the enemies sometimes dissappear in midair. also powerups are collected even if you are not touching them. i think you should work on the overall usability.
Other than that i like your enemy and boss design