All I have to do to indicate to other people who have finished it is go SPAAAAAAAAAACE. I like that. I am always a fan of the injoke.
Sooooo I do agree with Yahtzee's take that it's a little bloated. Honestly I would say that the major flaw to me was adding a new technology in the third act - suddenly you have to slow down a plot that's moving really fast towards a resolution to learn about the light tunnel things and restart the whole learning curve that you already did with the lasers/refractors and the light bridges in GlaDOS's act, and the three kinds of goo in Cave Johnson's act. Did it just seem symmetrical that Wheatley get to introduce a technology? Because I think if they hadn't needed to put the player back through tutorial steps in the third act, it wouldn't have seemed half as draggy as it did. I mean, the Cave Johnson bits were very good, very atmospheric, and I liked them a lot, even if some of the puzzles were fiendish and depended on internalizing the rules very very quickly or jumping into walls aimlessly for an hour while going AAAAAAAARRRGHH irl. I am planning to listen to the commentary on Youtube if I can, not play through again for a while (video gaming: good for my logic and spatial relations, terrible for my back), and I'm eager to find out if they added it then because putting too many new technologies into the GlaDOS acts made it crowded or hard to learn. Portal 1 was a delightful experience just because I tend to play Lady Games where you sandbox forever, and it was nice to have a forward-moving plot with pretty much zero grinding. But then I am happy to have a new Portal. I am told that co-op is honestly the best part, but there's only one Portal-capable computer in my house, so I would have to convince my brother to haul his up and then find another co-op mode virgin to play with.
The ending was crazy OTT. I SHOT THE MOON. Why did I shoot the moon? But at least Chell gets to live until, you know, she dies of all the toxic sludge she's been dipped in :( And apparently in the future in question there is still wheat! Wheat means people, with food, so that's good.
Overall I liked it! I think it was just the last three Wheatley puzzles were being done while I had a bad cold and just wanted to get to the finale already, so maybe I should have waited. If I ever do co-op I imagine I will enjoy it.
ETA: Incidentally, how crazy beautiful were the Turret easter eggs? I found two on my own, the Prometheus Turret and the Turret Opera in that one level where you use the lasers to set the turrets on fire. That made me feel pretty bad about shooting them. For like a second; things are terrifying.