Not a bad starting point, music was a bit loud and jarring, but overall not bad.
Basicaly took about 20-30 seconds to load (im on 30mb line) but it was sunday peek time. Music took longer i started the first game and music took a few seconds before it started.
Destroyed all the asteroids and a new level didnt start and the game didnt end, it just sat there spawning the ocasional alien ship.
If mouse isnt going to aim, I think it might be better to use space or x or z to fire... less confusion that way... just a thought.