I like IX's gameplay quite a bit. As for its battle system in particular, the slowness (compared with VII and especially VIII) and the relatively lackluster Trance system knock it down several pegs for me, but I appreciate its old-school approach to predefined jobs and whatnot. Then again, that's clearly not for everyone.
VII and VIII both have battle systems which offer me more fun overall though, I think.
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K | H | A | Q | Q | A | H | K
"we're about 50 years behind the rest of western society." -icon on B8