I completely agree with Yatzee on most counts, however, I did find that the multiplayer feature had one redeemable quality as far as replay was concerned: when my boyfriend and I replayed it to get the achievements, we did excellently working together and managed to wrap them up nicely in a very short time. It was enjoyable and we worked well together because we had played it before. I know this is probably a small thing, and if you didn't have achievements, then you wouldn't have this luxury. Nor would I want to play co-op with someone who hadn't played (I have zero patience and the bf and I raced to solve puzzles before the other one did). I thought it was worth mentioning because I wasn't sure if Yatzee was a secret achievement hunter, or if he's jaded enough by games to not give a $h*t about little electronic trinkets and sound effects pronouncing his awesomeness... Actually, now that I'm thinking about it, he probably gets that enough by reading these posts.
That said: Portal 2 was great, not because of the puzzles, but because of the story development. I've wanted to know more about Glados since the first game came out, and Valve was kind enough to supply while giving us several other lovable characters to appreciate. I have to agree the single player sequence lacked quality, but it made up for it by giving us a story that fleshed it out and helped pave the way for a delightful Portal 3 that hinted at everything from Glados taking over the world with giant turrets, to portals in space, to freedom on a desolate planet with only a portal gun and your wits and I, for one, cannot wait!