I love me some space shooters, so I had a blast with this one. My highscore ended up being 11675, which I feel isn't bad, but it definitely could be better. The graphics were really nice as well. Too bad there wasn't any sound.
One note I might offer, though, is I feel you should have included a lives system. The game is pretty hard already trying to keep the toxic waste from hitting Earth, but instantly getting a game over if you are hit by anything may make some players not as happy. This would be good as a hard mode, but not as a normal mode.
Other than that, I feel this turned out pretty solid. I didn't run into any noticeable bugs, and I had a great time playing it. Great work! :)