I don't think that I can really review Assassin's Creed. I'd just be parroting Yahtzee's review. (One difference: I actually enjoy the "chores" you have to do before the mission. It makes me feel like I'm controlling the mission, and that I can choose to get more or less information about my goal.) So I just have a few points to make that he didn't cover.
Unskippable cutscenes are a mortal sin. I am making this post entirely in the dialogue that cannot be skipped. It's criminal. I've beaten the game, but every time I start a new session, I have to listen to a rambling discourse on the nature of good and evil from a couple of jerks who are entirely unsympathetic.
The skill progression system is well regulated. You learn the skills at a good rate to not be overwhelmed, but always have some new tools. My one quibble is that you learn the parry move before the dodge move. The parry move basically makes the dodge obsolete.
Now that I've beaten the game, I can kill civilians without losing HP. I have to tell you, it feels awesome.