The player character enters a mansion, anticipating a party which is to occur there later. He cannot interact with the environment in the usual way - however, the mansion reacts to his presence, reconfiguring itself depending on his actions.
This is a fascinating game - especially at first, when trying to work out exactly what is going on. The lack of the ability to pick up or manipulate objects in the normal way seems frustrating initially, but it's easy to adjust to. One great feature is a notepad that tracks what the player character has discovered about the workings of the mansion - a nice touch.
The second part of the game has split reviewers more. This takes place in the same mansion, while aforementioned party is going on. The events of the party are fractured in time: the same characters appear in different locations simultaneously, to indicate their participation in events at different stages of the evening. The player must collect "intentions" and unite them with the appropriate person. In doing this, a murderous (albeit poetic) tapestry is unravelled.
I thought both parts were intriguing and original. The first is indeed a stronger concept and more satisfying to solve, but the second part is startling (and, in places, baffling) enough to make it distinctive.