Great game! I really like infinite/procedural games and this one is pretty addicting. The simple controls are a plus. I just think it could use a bit more content- more variety in enemies, more interesting weapons, etc. as you move up. Hopefully that will be a part of the full version. Also it's kind of frustrating how when you are down to one life it's very difficult to recover since you barely get any lift. It also breaks the flow a bit when you have to stop for a few seconds to refuel all the time but I don't really see any way around that.
As far as music goes I'm an amateur musician and I'd love to work on a soundtrack for this game. I'm not the greatest of all time but I think I can do better than this placeholder track. I can try to have a demo track ready sometime next week (assuming you haven't found someone else to do it yet). If you want to hear other stuff I've made my soundcloud page is also thrifstor.