It goes downhill after a few assassinations.
I was so amazed by the stunning graphics and the opening cinematic made me wanted to get started with the game asap.
The first 1-2 hours of the game would make you really absorbed into the game until you realize that you will be doing the same thing over and over again.
Travel to one of the cities, eavesdrop / save citizen / interrogate, climb buildings. I did 6 assassinations and got really bored with the game. It's too repetitive...
The flags are useless. The battles are easily done by countering.
You can actually win a battle with 10+ guards just by waiting for the right time to counter.
Despite it's beautiful environment and great story, Assassins' Creed game play did not work for me. I can't wait to get my hands on the sequel as it seems that they add in a lot of features in the game play.