If your talking about story related surprises, I would say that the part that surprised me was when Judge Gabranth removed his helmet and you saw that he was Basch's twin brother, and he framed Basch when he killed King Raminas. Yes, I'll also agree that the part where you discover that Balthier was once a judge himself was surprising. Also, finding out Balthier's true name was a bit of a shock, because the name sounds so silly to me (Ffamran mied Bunansa? Blech....thank goodness he changed it, lol).

Gameplay wise, I have to say that hunting marks turned out to be surprisingly addictive for me. I usually don't have a great passion for side quests in FF games, but this was one that really got into! I spent many hours questing for those marks, and I still have 2 to go.