Assassin's Creed, in my short experience with the game, stands out as having great graphics, a very immersive sense of spatiality, but lacking a little in the overall story-line. That may well not matter to most gamers, especially those for whom "the play's the thing." To them, only the repetition in certain quests (eg gathering redundant flags) may damper their enthusiasm. Running and climbing and jumping and kill and hiding like a medieval assassin covers a multitude of sins, as they (don't really, I guess) say.
So from a game-play perspective, I don't have too much to criticize. I especially like the "social stealth" aspects with the blatant mapping of low profile to socially acceptable actions and high profile to socially unacceptable actions. While the initial introduction of these features seemed a little cheesy, these game-play mechanisms served to emphasize the important elements of the game -- staying "hidden." I think making it explicit what people will tolerate made for an interesting design territory. If anything, I think they failed to fully mine this fertile ground. The protagonist's actions and methods could have been questioned and problematic. Instead, efficacy remains your by-word, and instead this seeming spiritual man seems to have no qualms about his actions, something either a ordinary Christian or Muslim of his time might have (and apparently the protagonist descends from a mother who is one and a father who is the other). While I'm truly delving into "you should source this properly land", it appears medieval assassins belonged to an offshoot Muslim sect persecuted as infidels by other Muslims, and whose main quarrels were with them. Nonetheless the Crusaders played a big part in defining them, so I suppose they can be the "big bads" of this game.
Oh well, enough of that. From this game, I derive the idea that explicitly linking your character's maneuvers to narrative goals seems like open design territory. Also, making up a ridiculous and pointless metanarrative that's approximately one micrometer removed from "it's all a dream" is dumb, even if upper management ordered it late in the design process and it wasn't really your fault and hey we've all been there amirite?