Not much in terms of gameplay. The scoreboard got revamped. There are some achievements. Character movement is slightly different.
Motion blur like other source games.
Achievements.
Slightly different grenade explosion sound when in the distance (like HL2)
Bomb explosion has been updated
New kill cam (like TF2 apparently but i havent played that)
Multicore rendering like other source games
I don't think they're changing much besides that. there's still heaps of bugs, especially with multicore rendering (stuttering)