Wow, really cool game! I really had fun and enojoyed the presentation. I have a few little nitpicks:
> enemies really close to the bottom of the screen felt a bit unfair
> later basic enemies had too much hp and were tedious to kill
> The rank is a bit unforgiving if you ask me. I didn't feel like i was doing that poorly but still go an F :D
Also, the kill count is kinda useless if there is no way to game-over and enemies don't despawn