GameTrailers TV also has their new preview of Portal 2 which includes gameplay footage from the upcoming platformer sequel and an explanation of some of what to expect from the game from Valve writer Erik Wolpaw. Along the way we get more details on the game's story and how co-op mode will work, with Erik explaining that gameplay is changed with four portals in play, and how if they find a way for one player to solve a co-op level, then it is considered broken.