On it's own it's a decent SRPG with okay-ish combat and a not-so-great story, but its real saving grace is how it's a dedicated love letter to the fans of the series, so if you're a fan yourself or interested enough in the series, then you might get some enjoyment of it.
Gameplay-wise it's the same as 5 with the only real change is that uses an agility-based flow instead of a phase-based one. The issue is that battles are slow and boring, map size got slightly bigger than in its predecessor, but everyone can only move only up to 3 squares so it takes a while for any sort of action to kick in, and magic is ridiculously overpowered here more than any other SN, aside from that it's passable overall.
There isn't any sort of actual overarching plot here, in a nutshell you're just collecting characters from other SNs who fell into some other world and find out what the heck is happening there, and save the world and whatnot. But the interactions between all of these characters from different times and circumstances over all sorts of topics and events from the previous games or even this one is the meat of the matter in that aspect.
And the less said about the localization (specifically the voice work), the better.