In "My life with Master" the party play the henchmen of an evil master. It explores ideas of culpability, fear, self-loathing, humanity and, possibly, redemption. It is the only role-playing game to give me heart ache. Literally, pathos I felt as a physical reaction.

"The Clay that Woke", another by Paul Czege, concerns a race of Minotaurs, more physically powerful but utterly subjugated by humans. It explores themes of racism, power, imperialism, and ethics. Not quite as good MLWM, but very much worth playing.

I added "The Beast" to go all in on a game totally unlike D&D. It is a single player game, using cards and a diary, with an erotic theme, and dark overtones. I haven't finished my play through, and I'm not sure I recommend it, quite, but it has got under my skin.

"Hillfolk" is Robin D Law's 'Drama system', essentially game mechanics built around generating interesting interpersonal conflict. The setting is Iron Age subsistence, but it includes several other settings, from horror to modern life.