The reason Video Games where created.
Playing through and just doing only the main missions I can see this taking me somewhere around 15-20 hours, but I am not one to just do that. I love getting into the game and collecting things and doing side missions. I can see myself spending at a minimum 8 hours in this first city, which is the smallest of all 3 that you explore.
The story of this game is, well surprising. Looking at just the movies and interviews and screen shots you would think this is just about being an assassin back during the crusades... there is a twist however.
It is present day, and you are captured by some big company. They have a machine, the animus (lol forgot how to spell it). This company uses this machine to access your DNA, and in your DNA they access the memories of your ancestors. This is then represented in a 3d virtual reality setting. So, basically you are in a machine, playing as your ancestor. Going through his memories of these assassinations. There is basically 2 stories going on, one in the present as this company tries to reach the memory it is looking for, and one as the assassin and figuring out why these 9 people have to die.
I could talk forever about this game, and I have only just begun to play it. I have not even gone into the technical points of this game, such as graphics and animation. There just isnt enough room on this page to go into it all, and ultimately you have to play it to see just how beautiful and great it looks.