I bought this the moment I could pre-order on STEAM, and played it the minute it was unlocked. I just finished it tonight, after playing casually between bouts of WoW.
WARNING: Spoilers Ahead!
Noooo! Not Robert Guillaume! Say it ain't so! I worked so hard to save him in Half-Life 2! Ah well. The game was short but sweet, with an ending that actually elicited an emotional response. And, they managed to tie in Portal to the plot. Nice.
Oh, and I believe Gordon Frohman from the webcomic Concerned made a guest appearance. (Even though he's supposed to be dead...) And, oh yeah, the LOST numbers appear on a PC screen in game, as well as a hidden Dharma Initiative poster. Very cool.
All in all, well worth the money for the game. I can't wait for the conclusion.