Simple, its so much better than the first one, more open. I didnt even make it through 13 because it bored me.
For what i can gather, 13-2 is what 13 is after the 20 hour mark, nice lovely open world, but at least with 13-2 you don't have to tear your eyeballs out from boredom before you can explore.
If you didn't like 13 (due to its horrid linear style and over dramatic storyline) and are questioning weather or not its worth getting 13-2. Seriously, just do it.
But still, all in all, they should stop with final fantasy games. They are slowly getting worse, i think they are just finding excuses to make things pretty >.>