What does FFXIII-2 do differently that merits a play through? I hated FFXIII fyi.
For starters, it's not a bunch of linear hallways. It has good zone maps that have a fair bit of exploration to them.
The job system it uses is also fully open from the get-go. You can level any class you want on Noel and Serah right away. How you level up the classes is a bit tweaked too - it's sort of like a linear sphere grid that you move through that repeats itself with bigger and smaller bonuses, but the class you currently are set as determines those bonuses and you can change your class at will. It works really well.
You still only control one character at a time like in FFXIII and it uses the FFXIII battle system, but unlike FFXIII you can swap between your lead party member in combat and aren't locked to someone.
Your third party member slot is for Monsters that you capture and raise. They each have their own specific classes and ability sets. You can also fuse them together to give a monster abilities of other monsters and it's a really fun system to play with.
There's no world map, but there's a Time Gate system like Chrono Trigger uses and it is pretty damned awesome. There's a ton of time jumping around and there's some cool changes between areas in different periods. There's also a bunch of Chrono Trigger-like "What If" endings you can play through by going back and doing specific things in different eras post game. Bosses you can fight again doing different things, etc.
There's tons of hidden shit to find and explore as well. Hidden monsters, puzzles and repairing time fissures, etc.
Oh, and they actually manged to make Hope pretty damned cool. He grew up quite a bit.