I had it pre-ordered a few weeks in advance.
I really want to talk about the story but I don't want to ruin it for people. Spoiler-free.
Easily one of the best games I've played. They took the brilliance of the first one and expanded greatly on it. There are plenty of new gameplay mechanics so the puzzles never seem redundant. The characters are hilarious. The dialog is well written and the voice acting brings it to life.
The co-op is very well realized. It isn't just some after thought add-on, it's a fully fledged game mode with more witty monologs from GLaDOS and rather challenging puzzles. It requires real team work to succeed in co-op, one player can't just carry the other through the game.
Only complaint? Hats. Really? TF2 has more than enough hats to cover Valve's headgear needs for a while. The co-op itself doesn't have a terrible amount of replay value so unless they are going to release more co-op content why would they include such a trivial feature?
Valve really took the fps to places it had never seen before and in a market flooded with Battlefield and CoD-esque games this is a much needed breath of fresh air. I can't recommend this game enough.
I give it 9.7/10
Now if only they'd get around to finishing Half Life 3...
i'm getting way too old for this shit 
