From the Rulebook:
In Betrayal at House on the Hill, each player chooses an explorer to investigate a creepy old house. As you explore the house, you discover new rooms. Each time you enter a new room, you might find something . . . or something might find you. Explorers change over the course of the game (for better or worse), depending on how they deal with the house’s surprises. The house is different each time you build it. At some random point during the game, one explorer triggers a scenario called a haunt. When the haunt is revealed, one explorer becomes a traitor bent on defeating his or her former companions. The rest of the explorers become heroes struggling to survive. From then on, the game is a fight between the traitor and the heroes—often to the death. This game has fifty haunts, and each one tells a different story. All are yours to explore as you live or die in the House on the Hill.I've been wanting to play this game for a long time, ever since I watched the play-through on Geek and Sundry's web-series Tabletop. Its a real fun game, and if you looking for something new I highly recommend it.
My family and I have played this game a couple of times now, and look forward to playing a lot more in the future. The game has tons of re-play ability, as each time you play the game its different, and the event end of being random.
Here are the links to the two part play that TableTop did for this game.