Aww, no mention of the audio and voicework? The music is brand new. Most of the dialogue has been rewritten, and recorded with some of the best impressions I've heard, period. Before the game really even started, before I got my HEV suit, I found myself wandering around the facility just to listen to what everyone had to say. There's a LOT of added dialogue, entire scenes that are totally unnecessary and in the background, and they all seem to mesh very well with modern-day VALV[sup]E[/sup]'s sense of humor. Top notch writing is one of the biggest improvements they've made over the original, IMO.
P.S. Thanks