XIII-2 is worth it just for the Arena introductory cutscene.
Serious talk though, it's a great game. Despite a few eye-rollers here and there, the story is somewhat solid, mostly mired by wonky presentation, but when you get down to it, it's actually quite a bit more straightforward than the one in XIII. I mean really, some movies get away with more plotholes than this. Meanwhile, characters are much improved, Lightning is almost not seen, Hope got way better, Serah and Noel's goals and motivations are simple and relatable, both are quite levelheaded and dare I say there's a bit more chemistry between them than in the entirety of the XIII cast? There's a bit more light-heartedness where it counts, probably because Lightning the Fun Vacuum isn't around. The entire dream sequence in the latter half of the game is actually genuinely well-written material and a highlight of the scenario. Also, Caius. Caius is a great villain. Comes with his own musical theme too, and what a theme. Most would agree Noel-Caius-Yeul substory is a high point of the trilogy. Watch these guys, it won't take SE long to butcher them to pieces as soon as the opening chapter of the next damn game. Soundtrack, while eclectic, is excellent and memorable, and regardless of how you feel about Crazy Chocobo, there's probably gonna be at least a few tracks for you. Time-travelling amounts to picking destinations from a menu, and it's not as open-ended as it could've been, but there's choice, and each area has enough diversity behind it to be remembered for something special. Monster hunting is almost universally agreed to be a good concept, and the game has a great speedrunning potential largely thanks to that system. There's minigames too, though they can be frustrating at times. Yes, areas are reused at times but that Academia though, can't wait to see that in decent image quality. System-wise it streamlined a lot of bad ideas from 13. Mog clock is a much easier to process concept than "sneak from behind on the enemy only 90% of the time it sees you approaching anyway at the last moment like it should"; ridiculously abstract upgrading system is practically gone; there's no punishment in form of long ass paradigm swap animation for screwing up the fickle switch timing and you get access to more roles and larger ATB bar so much earlier. Yes, it's on the easy side, but there's good potential for low-level runs and the arena DLC offers quite a challenge - I still haven't killed the last few encounters. The finale boss marathon was a gaming highlight of the last year for me.
I only wish this game was actually a standalone offering and not something that hangs between two lightnings awkwardly. I think the reception might've been a bit better then, as well.