This is a fun game. Having no limits to how far you want to go and how often is what makes it fun. The interface is simple but all look polished.
Don't know if it's only me that has no sound, but if not, then this game definitely need some. It makes a huge difference.
Also when I play, it's not full screen and the top part of the game is hidden outside of my screen so I can't see 1/4 of the game.
Just an idea, maybe you can add something the alien can pick up that will explode and destroy the asteroids in a small radius, granting extra points. It's fun to fight back :D