FF6 is actually fairly weak on gameplay, even I'll admit that one. Fortunately it was well aware of this and most of the time you'll spend playing is focused on story and characters, and the times you have to actually play the game they wrap it in some set pieces that have never even been challenged for awesome (tearing up Narshe in a set of Magitek, fighting the Phantom Train, the defense of Tritoch, the mine cart escape sequence, I'M JUST GETTING STARTED HERE).
FF6 had the best characters. FFX had the best gameplay. FF7, of all goddam things, probably had the most compelling - if somewhat muddled - overarching narrative. FF4 was probably the best for striking the right balance between story, characters, and actual gameplay, but it never specifically played to any of its strengths, so it stands out in far fewer minds than it probably deserves.
And FFXII... well, to be perfectly honest, it's too fucking long. It's the first (valid) FF to creep over the standard 40-hour mark and it perfectly demonstrate why these games typically don't. FFXII is fantastic in the beginning, where the plot is interesting and the system is fresh and well-balanced (and where you're only starting to get to know Vaan). It loses its luster as time goes on, and between 30-40 hours is where its welcome wears out. Had that been near the end, then it would be business as usual: you just grit through the last few dungeons, see the ending, and okay that's fine, write up your opinion. But that's the halfway point on FFXII, and that means that, in practice, half the game sucks.