What I'm seeing in Final Fantasy that constitutes to its stagnation is the Story-telling and music direction. When I played through XII I noticed how the music-direction in the game didn't have the energy and emotion of the other games (like when a character dies like in V and VII). In fact that's another point, storytelling.
There doesn't seem to be enough of that doom (a meteor in the sky) and gloom (kefka poisoning people) for "each" of the characters. The strongest part of any RPG is the story, and once the story just isn't as good as the ones you've played before, you start disliking the game itself too. Also, there's that linearity that's been in the games since X.
I liked X a lot even though it had linearity, but I didn't like XII. The difference was because of Story and music direction, which were way better in X. I considered V and VI, the pinnacle of all the Final Fantasies for these reasons: Mature Characters, Great music direction and Story Telling (quite unpredictable at times), and open world non-linearity. Also, a little more violence helps too, a maniacal villain (IE: Kefka, Sephiroth).
So in conclusion if the next game brings these things back into the game, then a lot will have to go wrong for the game to be boring.
It kind of gets me feeling like comparing XII to the Star wars prequels (please don't flame me for this sentence input, but I just had to add it in).
(Note: I have yet to play XIII or even XI-but that's an MMO anyways).







