in XIII-2, they had to recycle enemies and locations, because it was set in the same world of Gran Pulse as the first.
Lightning Returns has a nice story so far, and since it is set 500 years after XIII-2, there is all new.areas, and even some new baddies to fight! The battle system has changed, you solely plat as Lightning, so you switch between "Garb" which acts as a reboot of the job system, but enemies drop the skills and spells you need.
The only thing I hate about it as that they have a countdown clock like Majoras Mask :/ You only have so many days until the world just goes poof, so there is a in game clock so from 6 a.m. to another 6 a.m. you get to run around hoping to get things done, so if you don't know where to go, or if you want to find some hidden items, you'll just waste time and then waste the day, instead of completing the main, and side quests to boost stats.
I'll try to write a review, but I would like to beat it first, of course.
Anyways, about the combat system, it changed from a party of three to using only Lightning. You have like cameo party menbers, but you don't control them at all. It's odd. I'll get into it in depth when I scribble my crap out