Fun shooter!
I was confused at first and kept trying to load weapons/ammo clips onto a weapon slot somewhere. It wasn't clear that I should just grab a gun and run in. The ammo was confusing a bit too. Sometimes it felt like the rifle had infinite ammo and sometimes it ran out.
Some of doors allowed enemies to shoot you from behind the door before you can see them. I'm not sure which, but I would die a few times getting shot by an enemy behind the door.
I liked the multiple levels and how you incorporated the theme. Good job!