The physics in the game are amazing. There's a cutscene in the beginning that has a sort of hyperreal movie quality that's just chilling, and the facial expressions are quite expressive: there is one scene where Alyx is gently mocking one of the scientists, and she gets this silly half-grin that looks freakin' real.
And she has a great ass.
This pic doesn't do it justice.
Everything's cranked up a notch from previous installments, subtle but there.
And there's a new creature to fight. Hunters. Sonofabitch.
There will only be one more episode in the HL2 episode trilogy. Hopefully after that there will be a HL3.