To sum up my opinions on FFX-2:
The story is ridiculous and full of plotholes. I think the biggest nail in the Story Coffin is the so-called 'Perfect' Ending, which almost literally urinates all over the emotionally touching, beautiful end cutscene of FFX. Tidus' disappearance and the death of the Aeons were heavy emotional events which mattered. The 'Perfect' Ending flips all that around because...um...the Heart of the Cards did it? For that matter, is it ever explained why there are Dark Aeons again?
The graphics actually feel worse than FFX, and I don't know how they managed that. They might not actually be worse, but they feel it.
The soundtrack was sub-par for a FF game and felt almost phoned in by the crew. It's almost sad really that a game which opens up with a Songstress has such average and even bad music.
Blitzball was made worse. They had an opportunity to improve upon the game from its FFX counterpart, maybe add a third dimension like it should've had in the first place, but instead they turned it into a management game. Sphere Break was yawn-tastic and I felt even less inclined to play than Tetra Master or Triple Triad, and that's not even getting into the god-awful Calm Lands advertising stuff.
What else? Ah...characters. Bourne Endeavour summed up my feelings on Rikku, but all of them seem like they're almost parodying their FFX counterparts with Paine subbing in for the 9-months-pregnant-but-still-the-same-model Lulu. The dialogue is utterly terrible and had me groaning at line after line after line. JRPGs are cheesy and melodramatic to begin with but...jeebus.
Positives though were the Garment Grid system. I liked that you could change jobs for bonuses and you used it to unlock special dress spheres and whatnot. That was pretty cool, though I always found myself sticking with just one DS until it maxed out before switching to the next, meaning that I had less incentive to change until I'd maxed out all the dress spheres I was using. Better bonuses for switching during battle would have encouraged people to change around more and given more dynamic play.
It's not my least favourite Final Fantasy game (that honour goes out to FFVIII), but it's definetly up there.