Apart from being hilarious, this is actually the best review of Portal 2 I've seen. It's fair and balanced and makes accurate critiques instead of just gushing about how brilliant everything is. I agree with everything that's he said, and the mention of the un-replayability of the co-op is an especially frustrating truth.
I began co-op with a friend, and it was marvelous. We got through about 1/3 of it before we had to call it quits.
By the time I was able to get back and play it on another day, the same friend had already played through the rest of co-op with someone else (traitorous swine!). Even so, he agreed to go through my remainder with me. Except the exact thing mentioned in the review happened: since he knew every puzzle already, we blew through them, him dragging me by the hand, which was terribly un-fun and ruined the experience of figuring out the puzzles together. This is the same friend that I can replay the same L4D maps over and over with and have tons of fun, so it's not the person at fault. It's just the inherent flaw in having a linear, static, puzzle game with more than one player.
Why didn't I just play with someone else, you ask? Because within two days of Portal 2 releasing, every friend on my Steam Friends list had already beaten both the single player and co-op. I guess they are all in college or unemployed or something.
I STILL have one level or so left in the co-op that I can't beat because I have no one to play it with because nobody wants to replay it!