"It's one thing to out think a psychopathic computer program, as players did in the original Portal. But this brilliant sequel took things leaps and bounds beyond by asking players to out think one another. In a co-op mode to rival all others, players were forced to work together, but never punished for betraying each other instead. In a meta move, the real cleverness wasn't in the exponentially more complex puzzles, but in the way it asked players to trust in that Charlie Brown-like way that their friends wouldn't infuriatingly, comically sabotage them at the last second. Shooting your friends was simple; trapping them in an infinite, head-spinning loop was impressive." - Slant, 2014