I gave the game a 7. Graphically, it's almost flawless, with just an occasional stutter to mar things, but nothing to significantly detract from the visual beauty of the game. That said, my overriding feeling is that while they were developing the game, they were so caught up in rendering beautiful environments that they did not put enough effort into polishing the key component of a game: the gameplay itself.
AC has been criticised for being tedious, and justly so. Each of the nine levels consists of performing exactly the same actions as its predecessor, with very little (almost no) increase in abilities to make you feel a sense of character development. The game fails to instil a desire to progress, because the "levelling up" does not provide you with any significant enhancements over your existing abilities. (Admittedly there are some minor ones, but apart from the counterattack ability, which you get right after the first mission, there are few that are actually required to help you progress in the game.)
Because of the repetitive nature of its gameplay, AC has been compared with Crackdown, unfairly in my opinion. Crackdown did a fantastic job in creating a fun, addictive way to level up your character that made you want to go back again and again. Since you start off Assassin's Creed with pretty much all your abilities, you don't get the same sense of satisfaction as you did with Crackdown. For example, in AC, I never once thought "damn, I'd love to climb that building, but it looks too tall - I'll need to collect more flags to level up"...why not? Because I could climb every building right from the start. People complained about the tedium of orb collecting in Crackdown, but at least it served a purpose to the plot. In AC, the highly tedious flag collecting serves no purpose whatsoever except to cheat all but the most devoted gamers out of attaining some achievements. I like achievements, but I'll be damned if I'm going to waste a dozen or more hours roaming the land collecting useless flags.
The concept of the game is fantastic; the "play within a play" device is used very well, and gives context and explanation to a storyline that in other games simply demands suspension of disbelief. However, this plot device, clever as it is, can also be quite jarring and has a negative impact on the pacing of the game, and gameplay itself. After I've finished assassinating a guy and I'm pumped up after fighting off fifty guards, I really would like to keep going in my game world and explore the next section. Instead I have to sit through almost twenty minutes of unskippable cut-scenes to give a wholly unnecessary context to why I'm here. Often, games are criticised for lack of plot; AC's downfall is that it sometimes concentrates too much on it.
I must admit, I have not finished the game yet, so it may all come together nicely at the end, but for now, each time I exit the animus, I'm left feeling like I want to put the controller down and play something else. COD4, on the other hand, constantly left me wanting to go back for more. Even while I'm playing AC, a part of me is thinking "I could be levelling up on COD4 multiplayer instead of eavesdropping on yet another conversation".
Overall I think the game has some incredible components - the swordfights generally work well, and the free-running has been implemented almost flawlessly. The combination of this and the beautiful environments should produce a gamer's wet dream; instead, I'm just left with slightly damp pants, but a serious horn to see what Ubisoft can come up with for AC 2.