Love the take on the theme with this game!! Having it be first person also allowed for a really diegetic ammo display (literally watching your fingers fly off or reattach!) which is really smart.
The music did start to get annoying after a while, I know with SFX things like pitch shifting can help to reduce that although I'm not sure how well that'd work for this case.
The only other thing I'd suggest is having the floor a different colour to the walls / ceiling so its easier for players to quickly read the room layout and orient themselves (the terrain outlines are quite thin).
I love that you use verticality in your level design and overall think this is a genius game concept, well done!!!