This is an incredibly fun game!
The mechanic seems really simple at first, and then you run into the first red enemy. Having to scramble around picking up ammo, loading it into guns, shooting targets, and avoiding getting hit made for a really exhilarating experience.
Having extra treasure be available on each levels, as well as upgrades in between each level really gave some room for expression within the game as well, which is great.
All in all great job, thanks for making this game!