It's been pointed out already, but I think the cooldown timer is one of my biggest complaints, it really slows down the action. I'd suggest that shooting would instantly change your gun, but the cooldown will force you to change your gun if you don't shoot it, a "use it or lose it" type of deal. I otherwise think the art looks good and the idea is sweet.
I like this video a lot, if you're making lots of shooters, you might find it handy.