It's not a perfect game by any means, but somehow it just rubs me the right way. If you reduce it down to its basics, it's basically a big stealthy collect-athon, but the world is incredibly well-realized. The visuals are among the best I've ever seen, just slick as hell, and the cities in this game are both humungous and full of tiny details. I could do with some more variety in the citizens, and especially in their voice acting. I could also do with more variety in the sub-mission "investigations" Altair has to do before the Assassin's guild gives him permission to execute his mission. Speaking of Altair, why is he such a dick? I don't know if I've ever played as a character I didn't care for as a person. No matter, he does what I want him to, and that's what's important.
But back to the "investigations"--before taking out your mark, you have to hunt around the city for clues as to where they are, what they're doing, who their allies and enemies are, and other general intelligence. You only have a few choices: pick-pocketing someone with some kind of important document, listening in on an important conversation, following one of the mark's subordinates into an alley or other secluded place and "interrogating" them, or finding an Assassin's guild informant and doing whatever errand they ask in exchange for info. There might be one or two more methods I'm forgetting, but the point is that each assassination requires you to do two or more of these, and there are 9 assassinations in all, so you do the math. That's a lot of repetition of these little sub-missions. I've done 4 of the 9 marks so far, and I'm not bored yet, but your mileage my vary.
The other thing this game does a lot, for better or worse, is the collect-em-all thing. Each area in the game has 20 - 100 flags scattered around, and even though as far as I can tell there is no great reward (besides Achivement points) for finding them, I still can't stop looking around for them and going out of my way to pick them up when they're in such out-of-the-way spots as the top of an extremely tall church steeple in Jerusalem. There are also 60 Knights Templar scattered around the game world for you to find and kill (the Templars and the Assassin's are sworn enemies apparently), and lots of viewpoints to find and climb, as well. It's all fun and classic gameplay, but again lacking in variety. If you add up all the, lets call them widgets collectively, there are something like 500 widgets to track down in the game, if you are so inclined. But not much else to do, besides the killing of course. Again, fine for me (for one play-through, anyway), but your mileage my vary.
Let's talk about the combat for a minute. In the last Ubisoft action-adventure I played (Prince of Persia: Sands of Time), I hated the combat sequences, because the were interminable, innumerable, and broke up the good part of the game, which was the environment puzzle navigating. Combat in Ass Creed (a term of endearment if ever there was one) isn't the drag it was in that game. It's a good bit snappier here, and often completely optional. You're not required to rescue those citizens and fight all those guards, nor are you required to kill any guards who give pursuit upon recognizing you as an Assassin. You probably will end up doing it anyway, though, because the combat is pretty fun, and not hard to manage even if the typical scuffle is 4 of them to one of you. Altair has a decent set of moves, and a handful of weapons to choose from to break up the monotony--something the prince lacked.
So yeah, I went into this game not expecting much based on reviews and forum poster's accounts, but I've found it pretty enjoyable so far, and pretty impressive in terms of presentation. Check it out.