Art games are usually meant to reconsider rules, but often this reduces to just playing with conventions. "Sleep is Death (Geisterfahrer)" by Jason Rohrer, famous for his early controversial "Passage" game, is a little masterpiece of interaction. It allows two players to construct a story, but in a revolutionary way: one of them is the "computer", the other one is playing a sort of storyteller, able to create characters, write live replies on behalf of all the different characters except the protagonist and make things happening. Easier tried than told, this game is questioning the nature of video games: the computers AI engine here is a very sophisticated one: a human, and so if the two players are friends it would produce astonishing outputs (both have to react after 30 seconds maximum). The graphic is a rough 8bit, but nevertheless functional, because new elements can be quickly made, and it's evocative more than descriptive. It's a sublime mediation made through live computer game storytelling. In a word it's "improvisational theater as gameplay." And watching back the saved game is another interesting experience...