Love the game. There were times i found it to be a bit too easy. I think adding more ranged enemies would shift the balance as right now i think there are too many melee enemies, and they didnt really feel like they posed much of a threat.
Additionally i think adding a weapon that doesnt require ammo would be a nice fitting addition. I ran out of ammo in the middle of a level and almost couldnt find some. (thank goodness for the ammo dogs)
The boss fight was cool, and i think if multiple enemies spawned in (like 2 max) on the edges of the room, it would be a bit more challenging. Boss did kinda feel like a bullet sponge, but was really cool nonetheless.
Great job!