Betrayal at House on the Hill

THIS IS MY FAVORITE GAME.

Wait, you need some more information? Betrayal is a game for 3-6 players about exploring a dark and dreary house filled with all the greatest tropes of horror movies about dark and dreary houses. Midway through the game, the Haunt begins, where one player becomes the Traitor, gaining new powers and monstrous abilities in their attempt to defeat the Heroes. The Traitor and Heroes each have their own secret rules for the Haunt, and with 50 separate Haunts, no one can really know what the other team is trying to achieve.

Betrayal is random and wonderful and remains the most fun I've ever had with a single game. The latest expansion, Widow's Walk, adds new mechanics and 50 new Haunts, including one written by Yours Truly.