Not bad, but...
... I have a few issues. Firstly, your description is misleading. This is nothing at all like Galaga. Secondly, it's a little short, and there isn't much variance in gameplay. Third, if you play twice, the sound layers over itself. You need to end the music loop prior to starting it in order for this to not occur.
But like I say, not bad. a little more work, and a little more polish, and you're looking at a decent game here.