The plot was a little weak and slightly predictable. The protagonist aggressible alluded to something being wrong and thus the plot twists were fairly obvious throughout the whole game.
The fighting action is a little mundane and only gets hard in the last 3 missions. The jumping and climbing is fun but also very repetative.
As negative as the above sounds, the game has some pleasant predictability and is visually pleasing enough to play.
Overall I'd give it a B+ and would buy the sequel after a year.
By the way, the trailers on YouTube for Assassin's Creed 2 are fake