Not bad, but not long lasting.
The idea is pretty cool, but i don't think it has much staying power.
It gets a little repedative after the first 5 or 6 levels, and the music really doesn't help.
Perhaps either an alternating 2nd track, or a mute button for the next game?
I agree with the dude who reviewed before me, the grey background could use a little sprusing up, but i can see also how that would make spotting the asteroids tough.
All in all a good game, nice work.