Ever since the dawn of "Portal," the prospect of that gameplay with a second person is just slightly mind-bending. It seems the reality is just as mind-bending, as I attempted to survive a handful of "Portal 2" co-op test chambers with Valve's Erik Wolpaw.
Co-op features a completely different story and set of challenges from the single-player game. When teaming up, you'll control one of two robots...one made from an old GladOS personality sphere and another made from a broken-down turret. Your character doesn't affect your abilities, though, as both robots act exactly like the hero did in the original game.
Which means both robots can fire two portals each. So you can have a total of four portals running at once, and each robot is free to use the other robot's portals. Hopefully you're beginning to understand just how complicated this can become.
Thankfully Valve is known for its game balancing, and the challenges of "Portal 2" start out slow. But in time, the demands become greater and require constant communication between players. To this end, Valve added a communication system which allows players to mark objects in the world. For example, you can tell your friend to place a portal in a specific spot just by marking it...instead of having to painstakingly describe exactly where you want him to place it.
You'll need that communication when you come up against the myriad of new puzzle elements in "Portal 2." Laser bridges, refracting cubes and spring boards are just a sample of some of the new elements being introduced in the game.
From my brief play-through, it's clear that co-op "Portal" is going to be just as tricky as it sounds. But hey, that's why we play puzzle games, right?