I absolutely love that you made this, it's so so rad. I really love the music too, great choice!
I think some bigger visual/audio feedback when you fire would be nice, because I wasn't 100% sure I was shooting until I looked and saw the ammo was going down. Also, it's possible this is just a dumb unity/webgl thing, but the mouse sensitivity was crazy high for me, even when I turned my sensitivity all the way down on my computer.
The final thing is kinda nitpicky but I think that, since this game is like a DOOM parody, the enemy HP should be turned down. Enemies in the original DOOM are generally really easy to kill, and that's a big part of why it's so satisfying to just run around and kill those goons. I think making these guys die in fewer hits would make this game be like, a spot-on DOOM parody/clone/love letter!