Lots of the same good fun over and over...
Upon starting the game, you'll be slightly confused as to what exactly is going on. After you realize that you're playing a piece of dormant memory tucked away in your DNA, the game becomes rather interesting. Running around, bumping into people, playing stealth "lookit me imma ninja" for a while, and-- most noted of all-- climbing around on buildings and similar objects is fun for a long while. Even after you thought it would wear off, you can just pick off an innocent person or two and have fun with it while the guards chase you. (You know, "just so you can test your evasive skills." Which roughly translates to: you got bored. [already?!]) Well, nothing good lasts forever.
Luckily, just when you think you've had enough fun with the gimmicks, you get a new weapon or move or something. Something that makes it fun just long enough until you get your NEXT weapon. And repeat.
The story is pretty good-- don't get me wrong. When your main objective is to go out and assassinate some nine corrupt figures in a baffled society, so long as you put some thought into it before tossing it onto a shelf and telling the world you've got a great game, it's hard to make something like that into a turd-of-a-game. The only thing that starts to cook my noodles is that the storyline only progresses as fast as you want it to. You take longer, the game could get boring before you get to the next step (which, as mentioned earlier, would keep your interest and attention). On the other hand, if you just do what you're told and "git 'r done," then you'll have a hard time losing interest.
Overall, the graphics are gorgeous, the sound is amazing (try walking around in the cut scenes and rotating the camera-- see how that comes out of your stereo/surround speakers!), the story is good, and most of all, the gameplay is fun.