You know what this reminds me of? Gradius -- a primitive form, though.
The background can conflict with the foreground. Some of the enemies spawn on the very edge of the screen, and it's caused a death or two without realizing that they were there. This is more on the nitpicky side, though.
I'd say if you added more patterns, and enemy designs... possibly a new or different background, this would be a FANTASTIC minimalist game. I don't know if that's what you were going for, though. I like it a lot -- music and concept. The idea of a gem or point giver that spawns at the center of the, er, recoil, adds slightly more of a risk reward type factor, too, which I like.