Assassin's Creed was probably the best game I've played for the PS3. We played it to the point in college that we would actually have to stay away from the gaming system for fear of being tempted to play more.
The sequel should be no different. Visually amazing, this game really takes advantage of the system's graphic capabilities. It's just incredibly lifelike the way people act and move. The AI appears to be improved now and there are a number of Da Vinci's inventions to play with (such as the flying machine).
The whole thing takes place in a completely different time period so the environment is brand new. It looks pretty damn cool and could be in the running for game of the year.