Portal is witty, short, fun, original and in places really quite challenging. On the one hand, the game is very short; on the other, it has no time to get stale.
Buy, play, and love it, but only on condition that once you've done so you never mention either c-object or a certain song ever again.
Ever. Again. Those lines became stale four years ago. Repeating them now would be a travesty of bad taste. You have been warned.