Spoilers ahead.
I've beaten the game, but I'm curious about the "optional" places you can go, especially the locked room. There really doesn't seem to be any benefit of going in there since you use up all the bullets you get from that room on the enemies inside it and the ones you meet outside of it that just appear there.
Also, is there any benefit in saving or killing the non-violent npc's (usually nude ones) except for saving bullets? Is there another ending?