Red Dead Redemption - Undead Nightmare
First mentioned by Laggyteabag
The Old West, plus zombies. You really can't go wrong with that formula, and Undead Nightmare proves it. This DLC plays out separate from the main game, and pits protagonist John Marston against the living dead. After his wife and son are bitten by zombies, he ties them up and goes to look for a cure. The DLC also adds in mythical creatures that the player can hunt, including Sasquatch, the chupacabra, and a unicorn. Best of all, you can tame the Four Horse of the Apocalypse as mounts.