I just picked this up from my local store yesterday and played through a nice little sampling of it, and this looks like one great game!
Basically each player plays one of 7 knights of the round table. At the beginning of the game everyone randomly draws a loyalty card and saves it. In a full game there will be 6 loyal knights, and 1 traitor knight.
For the loyal knights, they must attempt to gather 12 swords that are awarded by completing quests around the realm. You can face the black knight, battle Lancelot for his armor, quest for Excalibur, fight off barbarian invasions, and of course quest for the Holy Grail. Each time a quest is successfuly completed a number of white swords (usually 1 or 2) is collected, while if the quest is failed a number of black swords are collected. While all this is happening players are forced to draw "black cards" every turn that advance the evil in the land and siege engines are also placed outside Camelot to signify the great siege being laid on the citadel.
The game ends when 12 siege engines have gathered outside the walls, or when 12 swords of any color have been collected. The loyal knights win if the majority of the swords are white, while the traitor wins if there are equal numbers or more black swords.
The interesting thing here is that most of the game is played cooperatively. That is you and all the other knights are working together to keep the realm intact, and not working together is the quickest way to fail. But you have to also learn who to trust... any of the other knights could secretly be doing things that are hurting the realm. You can out the traitor, but if you guess wrong it turns a white sword black, however if he remains hidden to the end of the game he converts 2 white swords to black swords (a 4 point swing!). It's hard to explain here, but the mechanics are beautifully designed to slowly increase the preassure on the knights and to make it possible for the traitor to keep his identity quiet while still hampering the goals of Camelot.
All and all it looks like a fantastic game. I can't wait to drag a few people in for a night of feudal fun.