The battles might be complicated for someone that's not used to JRPG's. The game does a really good job at easing you into the mechanics, but it can still be pretty confusing. If you don't grasp those mechanics, some of the fights, especially later bosses, will be extremely slow.
The story can be a little comical but underwhelming. It's a shift from previous games and has been described as more "anime".
The maps are large and confusing. Getting lost is extremely easy if you don't want to put the time into exploring and learning your surroundings. Monolithsoft has always created these kinds of maps.
I feel like those are the three biggest gripes of the game. However, I have over 200 hours into it and I'm having a lot of fun with it.