This is well polished! I liked the visuals and game mechanics. It was a simple premise (just spin and shoot) but having the other elements like air use, upgrades, etc really made the whole package better. Also the inclusion of the difficulty setting was awesome. I'd love some background music though, and hope you can include that in the future.
Some thoughts: I think it's better to be able to spin both ways though you'd probably have to balance this. There's at least a better sense of control from the player if you allow for this. You could also add different gun styles? like beam vs projectile with different damages?
Well done!