To my mind, the concepts of a believable world and believable characters are inextricably intertwined. This is why skeptics should be paying attention to whether or not their characters are more than empty shells with strong arms and good aim.Regardless what type of game you're making -- linear action or open world; action or RPG -- you're trying to build a world that players must believe in. Whether you call it a world, or you call it zones, or you call it levels, this is your goal: because one thing we do well, as a medium, is build worlds. But we must recognize that this not just down to the talent of the art team and the quality of their research and imagination.
via gamasutra.com