For me, X was fine with its linearity because of the story driving you forward. The idea of having to travel from place to place meant looking back didn't really make sense. This is why ultimately until the end of the game I didn't even realize that the entire game is just a huge line moving forward. That being said, I much preferred XII's world over X's.
However, with XIII, especially on the PS3 and 360, I found it inexcusable for the levels to be so small. It's often called a hallway simulator just because of how narrow and limiting the environment is. No one ever referred to X as that way, and for good reason. Grand Pulse was also a joke, it was shown and depicted to be a lot larger and more prevalent in the story, which was just false advertising, as the end product was just an open field of nothingness. I haven't even gotten that far into XIII before ultimately I stopped playing it because of how boring the entire experience was for me.
I think XII and Dragon Quest VIII did a great job of creating a game with worlds that were fun to explore while also being open. DQVIII had the world map with the towns and other areas being sectioned off, while FFXII had continuous map after map in large grid like formations where everything feels connected in a big world. Both experiences were fun to traverse and to explore while the linear corridors of X and XIII ultimately squash and desire of exploration.
Lightning Returns took a step in the right direction in terms of the map, but ultimately it doesn't really amount to anything at the end of the day... XV looks to have a world map that's diverse in scenery and looks to be much more enjoyable to explore. I think it will be more like FFXII if you took out the boundaries between areas.