I finished the single-player Portal 2
campaign, and I am very impressed at how it lived up to the expectations set by its predecessor, which I've long considered a "perfect" game, or close to it, and certainly one of my favorites of all time. I think that Portal 2 fits into both those categories as well: It's near perfect, and it also already ranks among my favorite-ever gaming experiences. I generally take my time when playing games, but this one I tore through voraciously, though according to Steam
I have played for 13 hours (I would have guessed a little less). This is in part because I know I'll play the game over again, and probably in part because I got into a "how quickly can I solve this" mode during a blast through the original Portal prior to the sequel's release, which I completed in about 90 minutes; including close to 30 minutes navigating through Aperture Labs for the final encounter. Anyway, the pacing of the game was great, the new puzzle elements like the gels were integrated very smoothly, Stephen Merchant and J.K. Simmons are brilliant, and some of the puzzles turned out quite challenging in a satisfying sort of way. Very simply, I'm making a note here: HUGE SUCCESS. It's hard to overstate my satisfaction.