The only thing I felt the game was truly missing, was CHALLENGE!
I BREEZED through Portal 2, only once did I have to really stop, REALLY look around hard and figure the puzzle out. (#28 btw)
I felt the game didn't allow you to make any mistakes. How so?
Go into nearly ANY test chamber and look at the walls, 90% of the walls can't have portals on them, this really makes it easy to figure out where you are SUPPOSE to put portals (simple deductive reasoning at that point), thus removing a lot of the difficulty, and hence, some of the fun.
I found most of my game fun from the EXCELLENT voice acting and story, but the actual gameplay was a bit of a let-down to me, I simply found it too easy.
I'm really hoping for a DLC with say, 10-15 test chambers with DIFFICULT puzzles, something that'll require me to spend some real time figuring out.
I beat the game tonight (I purchased it on Thursday), total play time was roughly 7-8 hours, I decided to play through it again the same night (wanted to check out commentary mode, which I enjoy), beat it again in 4 hours.
I think they really just over-tuned the puzzles too much, as told in the commentary, any time a playtester had a hard time, they made it easier...well, I think they over did it.