Oh, and one more thing: power-ups could drift instead of stay in one place. Could be more dynamic and you wouldn't be losing the illusion that spaceship really flies through space (not that bg is moving).
Seems really nice. I like the graphics, the idea of balls surroundering your ship that you can shoot is really interesting and I truly enjoyed it (something different!). What does game lack so far? First of all, music. If you don't compose yourself just get some music that you can use (Newgrounds.com have quite nice base of music that you can use under particular license). When game is paused it would be good to see "PAUSE" :) Personally I would like to see smaller number of power-ups. I wasn't able to remember half of them (optionally keep adding power-ups while the levels increase).
Good job so far and good luck!! :)
 "Deterministica"){kind=icon}
 "I Love You 2"){kind=icon}
 "Don't Look Back"){kind=icon}
 "Orbit Shooter"){kind=icon}