A subject I find really interesting is games that communicate their message primarily or exclusively through game design instead of through visuals or narrative. Good examples of this are Missile Command, Braid, and Dark Souls.
Huh, now I'm wondering if anyone has written a piece comparing framings of player agency in Bioshock and in Spec Ops: The Line
Bioshock is an interesting half-example because the game mechanics (emphasizing agency and choice) are a deliberate contrast to the narrative of acting without free will.