I'm sure you've seen the two loveable robots before, but this video should establish the personality Valve has infused into the two automatons and how GLaDOS will interact with them.
BOOM video 6378
The co-op portion of Portal 2 will be longer than the entire first game and is completely separate from the singleplayer campaign, which is also longer than the entire first game. Using simple math, this means that Portal 2 contains approximately 4,329.999999* times more content then the first game.
*Shacknews math not subject to validation.