Assassin's Creed
Assassin's Creed takes place in the year 1191, during the Third Crusade. You take on the role of Altair, a member of the Hashshashin sect (the original "assassins"). Your objective is to assassinate the nine historical figures who are responsible for the Crusades. As you find and kill these targets, you'll uncover their conspiracy.
There are three cities in the game world, Jerusalem, Acre and Damascus, each of which have been modeled with historic accuracy by using various historic references. The population of each city also takes on historic and distinct qualities, from the poor citizens to the upper class to the merchants. Additionally, all of Altair's targets are historical leaders who died or disappeared in 1191, although not necassarily assassinated.
The environment is completely interactive, from the climbable buildings to the people themselves. How you control Altair affects how the people around you react to your presence. If you discreetly move people aside to navigate through a crowd, it will not have any significant effect; but if, for example, you shove people, they may shove you back, resulting in unwanted attention from nearby guards. In a more extreme example, if you throw someone to the ground and kill him, the crowd could unite against you, forcing you to find a way out.
Another notable aspect of the environment is the openness of gameplay. In Assassin's Creed there is no single pre-determined path in which you must take to complete objectives. You can use the landscape to create your own path.