I liked the core idea, but it could be expanded on further. For instance, each time you charge a spin, you load a bullet, so I can load a couple of bullets at a time and kill an enemy uninterrupted. Or, similar to the enemies that shoot a spread of projectiles, your projectile spread increases the more you charge up at once. I wonder if you could add a mechanic where clockwise rotation is a pistol shot but counter clockwise is shotgun.
The core idea is so simple yet effective that you can explore it a lot. Kudos for the effort you've put into this game!