well, the multiplayer is fun, not enough to make me leave black-ops entirely, but still good. From what i understand when we get far enough we get to use parachutes, which i dont see the point of, but i havent gotten that far yet. We also dont dont go to any locations with ezio except rome, the villa once, and Firenze (during flash backs). That may be just a minor annoyance on my end though.
Leanardo is back creating things for you, and they make missions more interesting by giving you 100% sync goals. For example, one mission is to assassinate a templar without being seen, and the 100% sync goal is to assassinate him while sitting on a bench. if you dont do it from the bench you only get 50% synch.
Do enough missions at 100% sync and you unlock ezio's flashbacks.