Linear gameplay and linear story are also two different things. I categorize linear story as including story (obviously), but also subquests as well. This is what I feel is the design decision, and I won't get into a discussion about personal preferences. (Maybe in a few posts )

What I think about non-linear gameplay is having the world more open to you while you are completing the linear/non-linear story. In some games with 'non-linear' storys you are extremely limited as to what you can do aside from the established areas of 'non-linearilty'. Some games like FFT have strongly linear storylines (i'm not counting propositions), but inside of this linear story the meat of the game is just fighting and leveling your characters, a non-linear activity. Likewise a game like FFX was completely linear in both ways, I will give you that running along a straight path for 40 hours could probably be made into a better game experience.

In FFI there wasn't anything to do outside of the main linear quest, but there was excitement and exploration involved in just finishing the main linear quest. I think the problem now with linearity is that it lays too much out for you. Even if the story line is completely focused with no distractions, you have to feel like you are out exploring something new and exciting. (Something I feel 2d overhead cam/world map does much better then 3d 3rd person/linked areas).

Because lets face it, if your life was on the line in a world destroying chain of events, would you be running around being someones errand boy?