You could read on not having played Portal 2, but that would be ridiculous. The game is great. Just go buy it.
As I mentioned a couple weeks ago, Portal 2 features excellent pacing. You complete the most brain-bendingly taxing course in the game, and juuuust when it seems as though your patience might be getting a little thin with the way the game is playing out, it decides you're right.
"Surprise! We're doing it now."
From there, you're tossed into the endgame, and before too long, you're in the final boss room, where the game displays a little bit of fourth-wall smirking (Wheatley's not going to make the same mistakes that GLaDOS did, he's going to make completely new ones). Just when it seems as though you've beaten him, though, he has one last trick for you. Explosions happen, and all hope is lost.
Then it comes - the best scripted event in video game history. You're lying there, on your back, dazed. The roof of the center has been blown open, allowing you to see a sky full of stars and the moon shining brightly and...
I still have an open portal, right?
They couldn't mean for me to...
|Well, I guess it couldn't hurt to try...|
Nothing happens for a second or two*, then a glowing spot appears and suddenly all hell breaks loose. Air gets vented from the room, through the open portal connection to the moon and out into space, creating a vacuum that sucks you out. As you fly through, you just barely grab ahold of Wheatley, who begs to be let back in. GLaDOS severs his connection and snags you by the wrist as Wheatley flies into the void of space. (The flavor text for the end game achievement says it all - "that just happened".)
The whole scene is actually very tense and exciting, and the scene that follows (GLaDOS looking like she's going to kill you, then letting you go, then looking like she's going to kill you again, only the all the turrets to launch into some weirdly magnificent kind of robot opera) only solidifies the last fifteen minutes of the game as my favorite in game event in video game history.
Relive it below.
*The team apparently worked out the amount of time that it would take for the portal to get there, just one more reason that the people who worked on this series are impossibly awesome.