Taste the Cake

Awesome Portal music video. It is, however, a big plot spoiler for the game. I implore you to play the game to finality first as it's such a great example of proper game plot execution. It's short, it's sweet, and it's deep enough to rethink everything that transpired like a good novel.
It's what all good game stories should aspire too but frankly comes up way too short of the subtle masterpiece that is Portal.

Here's a great analysis of the game and some of the more sublime elements.