I just picked this game up friday and I am really enjoying it. The controls take a little getting used to, if your used to playing FPS games, and more recently hack and slash oblivion. I was rather confused at the customize control screen wondering where the block, and attack buttons were. I had to do the tutorial before setting my controls so i could understand what everything does. At first the controls seemed daunting, but I was quick to get used to it. As far as performance runs falwless on my e6750, 2gb ram, 8800gt system at max. Overall this game is just a blast. I like the free roaming ability, finding new and interesting ways to kill people. Story is good.
As far as negatives (mind you i havent finished the game yet) The Ive done 4 assasinations, and I can see that they are going to be repetative. Not the target assasinee part, that has been a little different, but basically the information gathering parts leading up to the assasination, are the same types of quests.
Next, once you get the controls down this game becomes pretty effortless (I mean I guess it makes sense you are supposed to be the most badass killer of the 12th century.) I really dont find blending in and stealth very necessary, as anythign that comes after me will be dealt with, without mercy (I find it more fun that way). Basically once you learn the counter attack ability, you have basically aquired the ability to kill multiple attackers with relative ease (but damn those counter attacks are some of the coolest death scenes in the game) for example with the short blade upon counter attack Altair stabs the guy in the foot pulls the blade up his body and slashes his throat.
Anyway as you can see even talking about the shortcomings, I cant get away from the good, dont let those things deter you from what is a very fun game.
Back to the good, the animations and graphics are amazing. Most every thing is really fluid. Especially the fights which adds alot more realism to the game, especially when your used to most games involving sword fighting being anything but fluid and smooth, but more jerky and unrealistic looking.
Altair can also, compete with spider man as far as scaling buildings is concerned.
Overall a great game, it has its short comings, but just a really fun experience.