This is incredibly contradicting.
If one game is enough to say 'Im done' then you never loved the series in the first place...
Huh?
That game took away a lot of what I loved about the older games. Overworld, a sense of openness.
And the games that came after that didn't bring it back.
I have to say though that around that time I got almost fully out of modern gaming. Didn't care for PS2, Xbox, GC or DC. I've always said FFX was the final nail in the coffin. Was looking forward to that if it would want me to get a PS2 after being gradually losing interest in new games. It didn't.
In retrospect FFX really was the game that ended my interest in future Final Fantasy games. Ok maybe you can say it can't be true if I had even a slight interest to see if FFXI continues that direction, but I don't think so. With FFX I still had actual interest in the game. Like, interest was maybe 8-9/10, it was that high. With FFXI my interest to see if it has gotten any better was down at 1/10. And with FFXII it was 0/10. Didn't even read reviews. I just wasn't interested even a bit. I was completely out of modern contemporary gaming when XXII was released. Didn't read new game magazines anymore. Game review shows on television bored me. Played with my Commodore 64, NES and PS1 + old and newer indie games on PC. For a while I thought that's how it is for me now. Whatever I saw and heard about any future Final Fantasies didn't bring back my interest one iota. When I got myself somewhat back to modern games in 2008 or so (thanks to Wii Sports) and I started to watch E3s and game news shows, new Final Fantasies remained just as uninteresting.
Up to FF9 the games had offered me pleasant overworld exploration (even though I think the overworlds in 8 and 9 weren't that great), progression that at least felt non-linear (none of the FF games aren't really
that non-linear, but at least they felt like it). So there I am, watching a friend playing FFX, walking a linear path after a linear path, no overworld anywhere to be seen. My interest towards playing the game went to zero. I don't care how good the story might be. If the gameplay loses the things I love in these games, then I'm out. The new generation of gameplay in video games just wasn't for me.
The number one thing that got me interested in RPGs was the idea of an overworld. The second is the sense of freedom. The third is the experience points. The fourth is turn-based fighting. There's a bunch of other things, like looking for treasure and grinding, before characters and story appears in this list. Even music comes before characters and story. So no matter how good story or characters FFX might have, it couldn't get me interested in the game when it misses several of the things I like the most on RPGs. So if FFX is the game where I lost all interest in the game for the first time and the following releases didn't even manage to get me interested into taking a look, then of course I say FFX was the one that ruined it to me. I can still play all of the earlier mainline Final Fantasies and have a good time.
If I would go and play some Final Fantasy game that came after FF9, it would probably be The After Years and I'm not sure if I'd really want to play that either.
As a side note, I think I saw the first signs of me losing interest in how games are presented and where they are going already when FF8 came. I liked the game and it's the last time I've been stunned by new graphics and animation, but looking at the back cover got me wondering what's going on. Screenshots showed only effects and cutscene pictures. Even in gaming magazines the screenshots of games felt increasingly more dull and confusing. I liked the game still though. Barren overworld but I had fun playing it (Triple Triad was great addition). With FF9 I started to see a bit of a decline in game design. Maybe it was already somewhat present in the earlier games but for some reason I started to notice the game going forward quite predictably. It felt fairly linear and I got better in predicting when the next boss appears. It got a bit tedious, but I still overall loved it (the card game was a huge disappointment though but I loved the Chocobo treasure hunt). Overall I think Final Fantasy 1, 4, 5, 6 and 7 are my favorites (not in that order). The rest are still good. But for X and beyond my interest is completely gone.