Very nice! Extremely polished, I love the text transition effects (where the lines extend and vanish, kinda).
The physics feel solid and act mostly the way you'd expect them to (although sometimes the wrap-around kinda confused me (I bet that was a pain to code, btw)). Once or twice, I got stuck in the middle of a large cluster of asteroids, seemingly getting sucked in as soon as I hit it, but shooting my way out was easy enough.
It does get a bit repetitive, yes, and with 9 lives, you can go on playing for a long time.
I only got two power-ups, rapid fire and spread shot (plus health once or thrice), and found them enjoyable. Rapid fire has a tendency to speed asteroids up to insane speeds, though.
If I may suggest features: (please ignore if the game is already complete)
Split the game up into three or four "worlds" of 8 levels each. Each world has a unique color, and perhaps different configurations of asteroids (plus world 2 is harder than world 1 and so on).
Have a mini boss on level 4, and a final boss on level 8, each unique for each world.
Add a scoring system, with combo bonuses and score power-ups.