Allthough I don?t like this type of games, I think your game is really curious, I like it :).
It?s simple, but works like a charm.
I would change a pair of things:
* The reload text size or style. I would change it for an icon or an alert instead of the big size above the enemies.
* The graphic of the lowest part of the screen. The Eath with the spaceship graphic. It?s quality is lower than the rest of the game.
Nice game anyway.
And like always, sorry for my bad english :).