i remember, I'd once played a flash game
it was a 2D top-down shooter where it had levels and no doors, and only 1 room per level
you were a white guy and could level up and buy guns and possibly also ammo, and, iirc, you could level up your guns
it had 16 or 32 bit pixelated graphics
there were boss levels
you started out shooting the undead, then you later started killing demons, and then, iirc, the devil
iirc, enemies spawned out of thin air, and perhaps in waves, or perhaps not in waves, and you could walk around the map, and could move and shoot at the same time
what was the game called?