A few optional extra quests that reveal more of the ongoing story or about the past (kind of like Lucrecia's flashback in the cave: you don't have to see it to finish the game, but it helps you a great deal to understand Vincent's story). Nothing that modifies or contradicts the main storyline, obviously.
A lot of good FMV's.
Rearranged music for real instruments (like they did in AC).
Dialogues with a translation as faithful as ever.
Marvellous graphics (of course).
Bonuses and extras galore.
Whatever.