I never have actually played Portal, and all things considered, unless it was at a friend's house or something, I probably never will.
That game's pretty much just one big first-person puzzle game, right? You just have align your blue and orange portals in certain positions to have you reach your destination? It sounds unique and interesting for a little while, but other then the whole "Companion Cube" and "The cake's a lie" thing, I probably couldn't play the game for more then five-ten minutes.