I just beat Portal. That was... very interesting. I did like the running commentary during the whole thing, though. (Edit: I just realized that running commentary could be misunderstood-- I meant by the computer-announcer person.)
I think it took me... oh, maybe 5 hours to beat it. I must admit, there were a few times when I didn't have any idea how to solve the puzzle. One of them I went and got a chair to stand on because I couldn't get a desk... Fortunately, after some smashing/banging, I got it to stand upright and make it work. :D
That's definitely a cool game.