I like the mechanics you made a lot, especially with the gun firing faster when low on ammo! Movement and attacks all felt solid, and I enjoyed it quite a lot!
I do think the overall design could be a bit nicer, though, since I was never really incentivised/able to go above the first floor because of all the muk dudes down there. They got overwhelming kinda quickly, and not in a super interesting way either, so I definitely think the enemies could be worked on.
Great job overall though, I had a lot of fun =)