I was recently listening to a podcast from a game developers conference, and there was a great deal of conversation around open world games like GTA. That discussion made me think about the difference between a storyline (be it from a book, movie or game) and the world in which it’s set. When a story is set somewhere other than the familiar every day world, the perceived richness of that world can make a big difference to satisfaction in the story. Think of The Lord of the Rings, where there is a strong impression that there is history to Middle-earth (read The Silmarillion to see that is exactly the case) and many interesting things are occurring just out of reach of the plot.
The first two Matrix movies are another example. The first Matrix movie was quite linear (as many prophecy movies tend to be). Neo was led from scene to scene to fulfil his destiny. The world around Neo was the same as our own except for two organised opposing groups who knew the secret of the matrix. There wasn’t much room for manoeuvre. Despite what people thought of the second Matrix’s plot, its world was far richer. Neo has some choice in his actions, there are portals or otherwise strange locations and rogue or independent programs roaming the matrix. It is no longer black versus white, there are many other actors on the stage.
When I used to run D&D games some advice I was given was to make the world seem as open as possible, even if you were trying to subtly guide the players in one direction. The story can be thought of as a train, starting at the caboose and ending at the engine. A linear story/game would have the protagonists/players just travel through each carriage in turn. In a more open environment they may travel by climbing over the carriage roof or skipping carriages by walking past them at a station or travel backwards for a bit. In a completely open environment they could decide not to go to the engine at all, leave the train and do something else. A world in which that last option appears possible and realistic is much more interesting, even if the actual story is linear.