Fun and intense game! I like the different weapon types and the variety of enemies. The charged shotgun one was my favorite, as it let me charge a really satisfying attack while I ran around avoiding the enemies. I also like that you progressively get more powerups throughout the game.
I'd add checkpoints in the game, because four health isn't a lot and it's pretty tedious going through all the rooms again if you die, especially if you get hit by those giant 2-hp bullets. I also think the boss has too much health, considering he only has one attack so I'm basically making the same movements for five minutes straight. Finally, the ranged enemies should wait a little before they start shooting. I noticed they shoot immediately when they spawn, which can cause you to get sorta cheap-shotted.
Fun game overall, I managed to beat the boss after a couple of tries! Nice music and cool 3d graphics too.