Unfortunately, though fantastic, the main chunk of the game is kind of a "Escape, escape, escape" feeling and then everything gets crammed into the end bits. Honestly, I would wonder if something was sacrificed for time or if the "end" segment was moved up a bit, leaving the remaining portions for the expansion packs and inevitable sequel.
Well put, I have the same feelings about this game. It deserves a lot of praise for doing so many things right and creating such a great experience but I really feel like Valve was feeling the heat to release this game and just started cutting scenes and features that were supposed to be in the game so they could release it sooner. Feels like we have a large part of the game, but not all of it. I'm guessing they are already working on an expansion pack to release exclusively via steam or something.