I'm five years late to the party but I've just finished playing Portal.
What a Game!
It was available on Steam for the Macintosh for just 8.99 or 18.99 euro for the Orange Box (Portal, Half Life 2, Team Fortress & HL EP1 and EP2) so I bought the Orange Box. I haven't really been paying attention to Games these past couple of years. GoldenEye for Wii reignited my interest last year. Portal was released in 2007 so by gamer standards it's old. I didn't know much about it but assumed it was just another First-Person Shooter. I was wrong. Many thousands of words have been written about this game - its writing is smarter and funnier than any other game I've ever played. The ending is very very special. I'm still grinning thinking about it. It's a glorious end to a brilliant game. Demented, Funny, Sad and Brilliant - I loved every minute of it. To get a feel for what the game is about go read Tim Rogers' review.
It used to be, chasms were the point of games; in Portal, they're just a casualty of the game's brutally inventive, genre-breaking concept. The only way to play this game is to break what you already know about other games, which I suppose is especially true if you know nothing at all about games. This game is vandalism for the gamer's mind; it breaks into the game design profession's ladies department at midnight and straps diamond dildos on all the mannequins.
-- ActionButton.net ~ Portal
GlaDOS, the computer who oversees your every move in the game, is one of the most brilliant villains ever written (in any medium, games, books or cinema). She'd eat HAL 9000 for breakfast.