I really wish you could go back to most of the game locations towards the end like they did with FFX instead of just a few Pulse areas. This is the major flaw about this game imo.
Villains aren't the game's strong point: Jihl was a huge disappointment, Yaag didn't get enough screentime and Bart was boring and generic. Orphan is basically one of those "No I'm the real final boss, not the guy who acts as the main antagonist" kind of final bosses (Necron anyone?).
I read the novellas so I know what happened during the "13 days", but those who didn't bother to will probably miss out on a significant portion of the story.
Why not just put that content in the game instead of few CS's here and there?
Another flaw is how simplicist weapon upgrading works, basically every mat does the same thing in the long run.
Finally, the game forces you to grind towards 2/3 of it. You simply can't beat 2m+ HP bosses that cast Doom after 20 minutes if you don't.
Now, for the good part...
Battle system is simply amazing, both fast paced and highly strategic.
I wish there were more spells and abilities available; kind of disappointed that there are no Holy, Flare, Meteor and Ultima. No big deal anyway. The game takes a "quality>quantity" approach when it comes to gameplay.
Summons are finally useful again. They're the ultimate "oshit" button, dealing both insane damage for most of the game and making the user practically invincible.
TP system limits their use so things stay balanced, which is a good thing.
Story and characters are above average, not my favourite but they made a good job in that department.
It's rather mature for a FF game, due the amount of violence and hints of a possible lesbian relationship.
Graphics and music are great as well, Oerba is by far the most suggestive place in the entire series thanks to them. Whoever says graphics don't matter in a RPG needs to be shot, because it would have been impossible to make something like that during the PS1 era.
Overall it's a solid game, not my favourite FF but not bad either.
If it had the amount of exploration games like FFVIII and FFXII had it could have been nearly perfect.