Overview
Portal 2 is a first-person puzzle game developed and published by Valve, released in 2011. It is the sequel to Portal: you solve test chambers using a gun that creates two linked portals, one entrance and one exit.
Story and world
You play Chell, who wakes up in an abandoned Aperture Science facility. Guided by Wheatley, a chatty little artificial intelligence, she tries to escape, but ends up waking GLaDOS, the AI that runs the tests.
The writing and the voice acting of GLaDOS and Wheatley are brilliant.
Gameplay
It is a game design masterclass: every mechanic is introduced, understood and then subverted without a single word of explanation. As the game goes on, the portals are joined by gels that make you bounce or speed up, light bridges, beams that carry objects, and lasers to redirect, and each chamber teaches you a new way to use them.
The co-op mode is a full campaign in its own right, with its own test chambers designed for two players, who play two robots and each have their own pair of portals. It is excellent. For my part, I only played the co-op, with a friend.
Verdict
A game design masterclass, brilliant writing and an excellent co-op campaign.