Just played for a few hours. The story is much more focused and driven this time around. You actually want to hunt these people down, not just because someone tells you to. As for the motivation behind it, I won't say anything in case people are on a complete story info blackout.
Some things I noticed right off the bat:
-The city is absolutely beautiful (Florence)
-The city feels much more lived in. Gone is the constant echo of "THIEF, I'LL HAVE YOUR HANDS FOR THAT!" You'll actually pick up unique chatter. I believe a Herald mentioned something about crop yields being lower than expected, so the florins per pound or whatever measurement he mentioned would be higher than usual.
-Climbing is MUCH faster
-Ezio is a bit of a sarcastic ass, but not nearly as bad as Altair. Ezio is very likable after you spend some time in his shoes.
So far the game is shaping up to be what the original should have. Now I don't want that to sound like this is a redo, it doesn't really come off that way. It's just a much more focused effort this time around, and it shows. After a while I found myself asking "What now?" much like the first game, but not for the same reason. In AC1 I asked myself that question because I had seen everything the game offered within an hour, here I ask the same question because I have so much to do, and so little time.