One of the great things about the Portal games is the inclusion of music. When I beat the first game, I nearly fell out of my chair as GLaDOS, the big, evil computer began to serenade me. And while knowing that she'd sing again in the sequel kind of made it less special, I still loved the new song, "Want You Gone."
But not, apparently, as much as the guy who made this video. To be fair:
If you haven't played the game all the way through, don't watch the video. But if you have, enjoy.