FFXII. I honestly have no idea how it got the great scores everyone handed out to it. I presume that was because they only played and scored it before the official release, and hence weren't playing it long enough to notice all the things that were horribly tedious and annoying about it. Then again, maybe it just seemed great to them because they'd never played another Final Fantasy.
I think the clincher that makes it the worst for me though is that all the characters (except perhaps Balthier) were ill-defined and completely unlikable. It just felt like a bunch of random, faceless people had randomly shown up to go on an animal-clubbing safari. For a franchise that relies almost wholly on epic storytelling, this is a fatal flaw. And I'm one of those over-analytical artsy dorks who, through rose-tinted hippie glasses, sees symbolism, subconscious psychological motives and deeper meaning in everything, so you know a story isn't being particularly well told when someone like me doesn't care enough to follow what the hell is going on.