I picked it up on release day.
As for extra content, there are two new dungeons apparently (haven't gotten to either yet), a new monster arena thing where you can train a monster and then fight it against other monsters to win items I suppose (I didn't do it much because it's not very fun). They also apparently added one more ending in. There's also an extras menu with stuff like a cutscene view, bestiary, etc.
As for actual gameplay changes, there are two control setups. One is essentially the original control setup, plus you can view extra stuff on the bottom screen like monster health bars and such. Then there's a DS control scheme that basically puts all of the menus on the bottom screen and leaves the top screen clean to show only characters and the environment. They also are using a new translation for this version.
I think that's most everything.