I can't find the article now, but there was a piece looking back at Final Fantasy X-2 and why it's secretly great. One of the big takeaways that I really liked: X-2 is one of the few JRPGs that answers the question of what happens AFTER the heroes save the world. Going back to all the places you visited on your pilgrimage in X and seeing how things have changed (sometimes not for the better) is one of my favourite things about the game. Spira feels more like a real world because of it, more complex and interesting than the bits you saw in X.
I also appreciate how goofy the game is compared to X. I mean, yes, Yuna deciding that what the world really needs to come together is a kick-ass concert is one of the dumbest things I've seen in a Final Fantasy game. And yes, I'm guessing back in the day that dumb massage minigame was supposed to be at least vaguely titillating. But, like, it's also goofy as shit that that massage minigame exists. And that second concert was pretty dumb, but the FIRST one that everyone seems to hate, the one with the J-pop song and the Charlie's Angels-style character intros, THAT intro is awesome and I won't hear otherwise.
That's not to say that X should have been goofy too, or that it suffered from being too serious; I think you needed both. And that's why I think X-2 works so well as a sequel; it's very much its own thing, but it's also a great complement to the first game's setting and tone.