Early reports have pegged Final Fantasy XIII as being a rather linear role-playing game, and Director Motomu Toriyama explains why this is the case to Ultimania magazine (with chapter numbers removed to avoid spoilers):
We made the map and battles function as part of the story, so that players get the same feeling as the characters. To achieve this, we wanted the story to progress non-stop [in a linear fashion], until Chapter X.
The interviewer goes on to ask if the game has fewer towns than previous titles in order to present a “non-stop” story:
Yes, it is one of the reasons, but more importantly, it is a result of considering HD graphics will be the mainstream. Considering the amount of work to make graphics that deserve HD, it is hard to make towns in the conventional style.
In the limited period of development time, to convey the the great story that deserves the name of Final Fantasy, and to convey the battles that entertain players enough, we condensed each element.
“Limited development time?” One can only wonder what they might have done if they’d had more than five years to make this game happen.