It has single, and multiplayer co-op modes.
The single-player portion of Portal 2 introduces a new cast characters, fresh puzzle elements, and a larger set of “devious test chambers”. Players will explore never-before-seen areas of the Aperture Science Labs and be reunited with GLaDOS, “the occasionally murderous computer companion” who guided you through the original game.
The game’s two-player cooperative mode features its own entirely separate campaign with a unique story, test chambers, and two new player characters. This new mode forces players to reconsider everything they thought they knew about portals. Success will require them to not just act cooperatively, but to think cooperatively.
Why aren't you pre-ordering right now?