Minor suggestions, otherwise perfect
First, great game. Major style points for the simple, intuitive control scheme (always a plus) and I LOVED the way the screen shook as your ship attacked. Gave the game a good action feel.
Obviously, the graphics were a bit simple, which didn't bother me all too much. My only gripe was that as your laser got bigger, it just seemed to look cheesy. Maybe you could find a more suitable way to convey power than just going with straight size increases.
I recognized a few of the sound effects, but the real reason I docked you style points is because the music was slightly repetitive. Okay, it was VERY repetitive, but repetitive isn't really bad as long as it doesn't get annoying. I just wish there had been a bit more to it.
Other than looks, the only thing that could've made this game more interesting were expansions on the gameplay, like scattered bosses (one every 48 waves?) and maybe a few, rare balanced power-ups. Again, FEW, RARE, and BALANCED were the key words there. Nothing ruins a game like an overpowered character. Also, I rarely if ever used my shield and managed just fine (on Hard difficulty), so maybe things should be a BIT more difficult.
Again, let me stress ... GREAT GAME. Didn't want you to feel like I was just bashing you for nit-picky things.