There will be a high degree of interactivity with the environment. For example, if you shoot a tree then it falls down and you cant hide behind it anymore [unless a player lies down], if a tree falls across a road a jeep cant drive across it, but a tank can. They (the trees) can fall on someone's head and kill or injure them. It is a very complete game (world). If a tree lies across the road then the AI knows this and stops the jeep, the ability to destroy the world is not just a side story but is crucial to game play.