Decent game, I have some suggestions, but most of them have been covered in other comments. One thing though, running Firefox/Mac OSX and the game loads w/ an all black screen about 40% of the time. Have to reload frequently to get started.
I had considered putting in SFX, but after playing the original "Space Invaders" I felt like they were an mostly annoying nuisance. Also, I put this together in about 2 weeks, so SFX was low on the priority list. Thanks for your feedback!
Also, I see that a couple players have made it to waves 9 and 10 already. The current difficulty caps out at wave 6. The next update will include some difficulty adjustments on higher levels for more advanced players.
@AngryGerbil I hadn't considered that, and it's a good point. I will definitely look into implementing two optional control styles for the player, mouse and keyboard. I'll include that with my next update.
I really like this concept, it's a lot of fun to play initially. I would add a pause feature, for sure, and maybe try to come up with a way to modify the somewhat awkward controls. Really cool concept though, 3-4 out of 5.
 "Man in Gap"){kind=icon}
 "Spikee"){kind=icon}
 "Crash Space"){kind=icon}
 "Arkandian Crusade"){kind=icon}
 "Space Attack"){kind=icon}
 "You Will Become..."){kind=icon}
 "Space Invaders Twist"){kind=icon}
 "Bull in a China Shop"){kind=icon}
 "Age of Defense"){kind=icon}
 "Epic Battle Fantasy 3"){kind=icon}
 "Solipskier"){kind=icon}
 "Sushi Cat The Honeymoon"){kind=icon}
 "Bubble Rasing"){kind=icon}
 "Hobo Prison Brawl"){kind=icon}
 "Platris"){kind=icon}
 "Zombie Exploder"){kind=icon}