If you make a thread about why nobody gives credit to FFIX in an FFIX forum then your obviously going to get comments like "I love this game its the best!" It was a good game I'll give it that but I'm unsure if it was the best FF.
The cutscenes in this FF were much less moving than in the other Final Fantasies. FFX had some great parts, for instance, the ending, in macalania forest, and at Yuna's wedding. FF8 also had some touching moments where Squall rescues Rinoa, or when they are on the Ragnarok, or when Edea throws the snowball at Squall. FFIX had a few decent cutscenes but the game in general lacked some moving parts.
Also the sidequests were worse than other FF's. The card game was annoying, even if your card had higher stats your opponents card can flip it? The FF8 card game is much more straightforward (aside from the regional rules part). And the chocobo mini-games in this version were all luck and grinding. Just hitting buttons and trying to find treasure in the same forest for hours straight and then going and finding chocographs. The breeding and raising and racing system in FFVII was much better.
Also the way characters learn abilities was kind of annoying. You might have to equip weak armor/weapon in order to learn an ability if you missed it and this would make it difficult to win battles and gain AP.
By all means, this is a great game. But VII, VIII, and X are all better imho. At least we can all agree that X-2 is still the worst game :P.