I agree with your praise of X-2.

Much of the criticism of that game comes from people who played it for an hour or so, then decided that it is superficial and 'girly'. I can well understand how they'd come to that conclusion. However, the game has a wonderous level of depth that only comes from perseverance and exploration. I didn't unlock all the mysteries of the story until my second play through the game.

The entire back-story surrounding Shuyin is really quite moving, for me. Unlike a lot of FF villains, he's not really a "villain" as such. In life, he achieved a lot - a musician, an athlete, a warrior and a deeply devoted lover. The agony of his unjust death, an agony so great it bound him to this world and wouldn't die. A millenium of detached thought, wandering rage and bitterness at the senseless loss of life. Then the coming of Sin, and even more death, but at least a sense of purpose and unity. Then, only two years after Sin's defeat - barely the blink of an eye - and Spira's on the verge of self-annihilation again, like nothing's been learned from the past at all. It's easy to understand why Shuyin would believe that the world's destruction would be a fitting punishment for the depravity of its inhabitants, and the only way to stop them from finding excuses for killing each other for eternity.

The game's darker themes work very well. The way Spira's moved forward with the coming of the Eternal Calm, but lost a lot of what it had. Cheesy commercialism and aggressive business rivallry have replaced the self-sufficient, communal living of before; Summoners, who spent a thousand years giving their lives to provide Spira with a few years' peace, are treated as worthless relics by many. With Yevon's downfall, the people elected to abandon all of the teachings, even those which serve a good purpose - the restriction on Machina, for instance. Unfettered technological experimentation is back again, the very process which led to the terrible weapons of the Bevelle-Zanarkand war. Even the Machine Faction, who ought to know better, spend most of the game working on their "Experiment", a device which serves no purpose except to be the most powerful weapon ever created. Extremely stupid.
So the game effectively shows just how ignorant and greedy people can be, how exciting and shiny new ideas can corrupt long-standing values and turn people against one another.
Just because the world was saved from Sin, doesn't mean that all troubles are over. A realistic concept. The Ronso-guado conflict is yet another example of that.

But then, there are the themes of hope, too. Optimism, positivity for the future, even though it won't aways be a rosy one. Yuna's significanty disillusioned with a lot of what Spira's become, but still fights for it and believes in the inherent value of preserving memory and freedom in the face of conflict and change.

Deep themes all around. A good cast of characters with believeable flaws, something I feel is important. Great glimpses of the past, too - alternate looks at what happened in the previous game. A completely new approach to an FF, which is understandable since it's a direct sequel. Instead of some lonely male warrior-type getting thrown in the deep end in a world-shaking conflict, we instead start the action from the point-of-view of a team of young women who're seeking their own ends, including adventure, exploration, discovery and research, with a bit of profit thrown in. Rather than being flung into the world's conflicts, they stay on the periphery, until such time as their intervention is actually required. And for once, there's no "evil empire bent on world domination", a la Shinra or Gestahl; instead, the political organisations - New Yevon and the Youth League - are both comparable, if both misguided.

A completely refreshing change, with new ideas and approaches to things that have spent the last decade becoming formulaic to the point of predictability.

There's also plenty of self-referential material to provide long-time fans with a tip of the hat; subtle and not-so-subtle hints of FFVI, VII and VIII pop up where they'd be least expected.

FFX-2 is not without its flaws, but I've mentioned those elsewhere. The game's doing a lot of things right, in my opinion. Not perfect, but innovative and fresh, and even if those innovations aren't all to my taste, I still approve of creativity.