Shit.
I think the story are much better than FFX's so far, but then again, I liked FFX's story a lot until they revealed the stupid ass plot twist about Tidus being a dream. The story is heavy handed stuff, and it has light hearted moments that help you feel good. It's a pretty depressing story, and personally, I think so far it's live up to its potential. Don't understand why folks think the story is so disappointing or why LO didn't live up to its potential story wise, but then again I haven't beaten it. As far as characters, I dunno. I liked FFX's characters so it's hard to say, but I guess it depends on preference. You may like them a lot more.
It's linear like FFX so far, but unlike FFX, you can actually go back to locations you previously did easily without an airship.
Gameplay wise, it is much better than FFX. FFX was pretty easy for the most part, but LO's got more thinking in it. Plus, your characters (immortals at least) are entirely customizable in any way you see fit, and this can alter difficulty drastically. However, FFX also has amazing dungeons with unique puzzles. Until the dungeon I'm currently in, LO has been pretty light on the puzzles and dungeon shit, but it's starting to pick up. The ring system is awesome, and quite simlar to FFX's. Like, I recently mixed my poison ring with a few other rings to make a ring that not only poisons enemies, but also does critical damage more often, and heals some hp when ever I hit an enemy. That shit is straight out of FFX and very similar to its weapon and armor system. Still, there's nothing as cool as say, making your sword Stone based, adding a counter attack ability to your character, and then STONING EVERY ENEMY YOU COUNTERATTACK like FFX. But hey, who knows.
That's a pretty tough question because Final Fantasy X is my second favorite Final Fantasy and LO is topping it in many ways. That's saying a lot.