THE CAKE WAS A LIE

[RickySteelo]

I had so much fun with this game but what if the game ended nicely at the end like you got cake and GlaDos left and you surfaced the earth at the end.

[Bellomy]

In fact, before they added a patch to the ending, it DOES end with you escaping to the surface! Taken on its own, apart from Portal 2, the original pre-patch ending is one of the most satisfying moments I've ever gotten in any game I've ever played.

The reason you're dragged back in is to set up for Portal 2. If you want to figure out whether or not you get the happy ending, I'd play that.