This makes sense, because the multi-player's higher degree of intricacy causes gamers to die far more often. Not only will there be four portals to manage instead of two, but it'll take more brainpower to wrap your head around the new puzzle mechanics. This added complexity once prompted Valve to say that a multi-player Portal is "less fun than you'd think" though that was two years ago.
To prevent players from strangling their partners, the developer is implementing a number of communication aids, such as a marking system that gives players the ability to show one another where to stand or where to place a portal. All in all, Joystiq said Portal 2's multi-player aspect is better than expected. The title is due sometime next year for Windows, OS X, Xbox 360, and PS3.