Valve did a nice job of keeping her from being entirely one-dimensional, though, as you get to hear a tinge (and perhaps more than a tinge) of fear in her voice on occasion. GLaDOS herself is hilariously sociopathic as always. A few spots demand more in terms of twitch skill and timing than Portal 2's single-player campaign, but the manual dexterity requirements aren't as steep as in the original co-op levels either. I was glad to see the return of the underused white gel for one long segment, and the addition of buttons that turn off Material Emancipation Grids required some new tricks to make it through GLaDOS' latest diabolical challenges.

As always, the excellent HUD indicators partners can bring up for each other make working together easy, even if you're stuck with text chat instead of voice like my partner and I were today. It skillfully combines all of the wonderful puzzle elements that made Portal 2 amazing to begin with into new configurations that will bend your mind even if you've played Portal and the sequel to death. The new co-op campaign, however, is brilliant. Both are up to Valve's usual sky-high quality standards, even if competing for speed runs is something I don't see much appeal for in Portal 2. The just-released 'Peer Review' DLC has two components: a two-and-a-half hour long (or so) cooperative campaign accessed through a new passage in the co-op hub, and a challenge mode with matching leaderboards for both single-player and co-op.

This free DLC pack is easily on par with what other publishers would charge $10 or more for.

I just conquered the latest Portal campaign with a random stranger on Steam, and it was glorious.

Portal 2 singleplayer coop