The music is really good. I like the idea of the game and the style of the art. I hope you add more gameplay/levels/goals later.
A few tips:
The ship does act a bit strange when the mouse is right on top of it, I don't know if that is easy to fix.
The cost of the upgrades isn't very clear. It doubles, but sometimes you lose count and you don't know when you will be able to buy them again. Maybe you could show that inside the upgrade boxes.