I absolutely love Portal and can find a Portal reference in anything-from the stands on mannequins looking like Chell's long-fall boots (from the first game-if you can call them boots), to simple things people say.
[SPOILERS ABOUND]
My favourite part of the game was the ending. Where Chell took out all of the corrupt cores, and saw their different personalities, then burned them in a fiery abyss C:<
How long? Probably a weekend and part of Monday.
I don't really remember my first impressions of GLaDOS that much, but I remember I just thought she was a robot with kind of a human/non-professional way of explaining things, if not a bit sadistic.