If they've really made the dungeons more open and less "oh god, which room is this they all look the god damn same" then consider me a happy camper.
I think Graces suffered more in terms of "dungeon sameness" and walking corridors n such, but every so often there'd be some 'trick' or something to do. Problem with Xillia dungeons is they're pretty big..... but there's also, literally, NOTHING TO DO IN THEM. You walk. And you walk. You jump up a ledge. Then open a door.
There's also, I think, more towns than fucking dungeons.
Also, I read up some spoilers on Xillia 2 --- NO I WON'T EVER REVEAL ANYTHING ABOUT IT EVER -- But I think there was *way* more time and love put into that game's plot.
Ah, I haven't gotten to play Graces yet, so I wouldn't know. ^_^; I'll be tackling it before Xillia.
I'm replaying Abyss right now, and it's a lot of the Sephiroth dungeons that are looking samey to me. Though if memory serves me right, Symphonia and Legendia was a bit worse in the whole "every room looks the same" department. It's been like 7+ years since I've played either of those though.
To be fair, I think it's a 'resource thing' that companies often make same-looking dungeons. Diverting it is a pain in the ass, and probably easiest when background were pre-rendered.
Graces' problem was more an issue of 'suffocating design', where dungeons were more corridors-meet-mazes. They're not bad, but certainly the days of Symphonian-esque dungeons seem to be behind the series.
With respect to that, my problem with Xillia lies in that dungeons aren't so much as long, or maze like, or anything else.... just that there's nothing to do.
These days it's like they fired whoever works on dungeons and just hired a few more battle programmers. YMMV.