Finished it couple of hours ago and I'm still like "WTF dude, why did you do that".
Game could very well be named AC3 with its amazing story and game time, the only reason I can think of for not naming it AC3 is that we play the same assassin as the previous game.
Anyway, I loved the game and the end was just as awesome as the other 2, maybe even better. Game has improved significantly. You get to make your own assassin's league and own stuff around the city. If you haven't played it yet, you're wasting your time playing wow =)