I think that the characters have to be interesting. I don't really care if they are developed at all.

FF4, for example. They don't tell us much about the past history of those characters during the game, but still, I love most of them. They have interesting personalities, and it's fun to feel it in the dialogues and stuff.

But since FF7 the characters are getting boring. I'm not even a FF7 fan (in fact, I don't like it), but it had some good (not that good), interesting characters, FF8 was a total disaster, and in FF9 most of them are too childish and silly, so I don't take them too seriously. I never played FF10.

FFTactics had a good amount of great characters, being the only Final Fantasy game I like since FF6.

But I don't blame Square... They are, at least, trying to create new stuff. Their new stuff is not good, but hey, it's new. Heh.