(based on the 10 or so hours I've spent in the J version)
It's good, but could have been way better. I wish they've changed the layout of some caves and areas, FFIV is a 17-yr old game and began showing its ago long, long time ago. Game design mechanics have evolved long time since then, there was no excuse to leave them so copy-pasted like. It would've made it so much more appealing to those who've played the game already (kind of like Resident Evil GC over the original).
I think a good example of how old the game design feels happens right on Baron Castle - you hit the blatantly-obvious switch over there and the wall just DISAPPEARS. That "rock door" on the beggining of FFIII's cave slowly dove through the ground, yet the wall in FFIV simply evaporates - just like it happened in the original game. You see where I'm getting at?
Cutscenes and narrative are way better tha original and the AutoBattle is a gift from God, but damn, how I wish they've changed those boring and archaic dungeons.