The co-op doesn’t have as much dialogue as the single-player campaign, but it still has a beefy amount over the course of five testing facilities, all of which from GLaDOS or the turrets (also voiced by McLain).  Each testing facility has a series of eight to nine chambers, some of which being two parts. Though this is a co-op experience, it is not a short one. It can take a good four hours to complete, give or take, and the fun never lets up.

Unlike the single-player, the co-op starts out with the Calibration Course, which is a series of simple tests to get you and your partner in “sync” with one another. It’s a simple and yet effective tutorial and it’s a good way to introduce players to the co-op mechanics. Each player will get two portals each, Atlas with blue and purple, and P-Body with orange and red. It’s essential to learn how to use your portals as well as your partner’s to be able to complete these courses.

Cave Johnson (voiced by J.K. Simmons) giving a sample of just what might happen in your co-op playthrough.

Upon completion of the Calibration Course, you enter a hub world of sorts, which is unique to this mode and fits the game very well. It reminds me of some of the hub worlds in old N64 platformers where there was a slight challenge to getting to an area. As you start the first course, it becomes clear that these stages were designed for four portals. It’s true that some chambers can be solved using only one player’s portals, but those ones still require two people to do. The level design is completely different than the chambers in the single-player and there are even features unique to the co-op mode. Features such as diagonal light ramps, spiked crushers, and even a few puzzles that require timing from your partner. Thankfully, implemented a marking system where you can signal your partner with a marker that would show them where to stand, where to make portals, buttons to press or even a 3-second timer for counting down the timing exercises. Even if you are using voice chat, these markers are very useful and work very well with the game.

Like the single-player, the co-op is full of Easter eggs to discover, most of which give you achievements or trophies. These are pretty fun to discover and it creates a humorous sense of accomplishment when you find them, my personal favorite being the hidden companion cube in one of the test chambers.

Each course will have a series of test chambers, and then a final challenge that will have you and your partner outside of the test chambers and in the main facility, searching for the data disc. There is a slight story to the co-op, but it’s mostly explained through the fascinating developer commentary, and its great to watch this universe unfold through it. To summarize, you are doing test chambers that no human has done before, in a sense, testing for the real test. I won’t spoil too much, but the ending is a bit funny if you put all the dialogue together.

All in all, the co-op experience is something truly unique and is a lot of fun to go through with a friend, either through Steam (PC, Mac, or PS3), Playstation Network (still down as of this writing), Xbox Live, or split screen (PS3 and Xbox 360). A nice feature is that the versions running Steam are all cross-platform, so PC users can play with Mac users, or PS3 users with PC or Mac users. If you buy this game, there are a lot of options to be able to play with your friends. If I were to rate the co-op experience, it gets a solid 9 out of 10. Very well thought out, and fun to play, even when replaying the chambers.

Two great experiences in one package, I can see Portal 2 being up for game of the year easily, at least for PC. When single-player and co-op are combined, I can give my final verdict of the game, and Portal 2 receives a 10 out of 10. Great gameplay, entertaining dialogue and sound, fantastic art direction, amazing presentation, and a game that deserves a spot in everyone’s library.