I've only played 2.5 Final Fantasies and seen FF1 and bits and pieces of a couple others, so I have a slight lack of experience with Final Fantasy. Despite that, what I want is a focus on a really good story with actual character development (heck, I'll just come out and say it -- I want likeable characters.) and beautiful music. (come back Uematsu!)
The stories (from what I've read/heard) have become cliché and boring, so I'd like to see an innovative, creative plot. Also the characters are bland (again, so I've heard). I only like a couple characters in FF10, and in FF12 I don't have a favorite character because I don't LIKE any of them. So I'd like to see some really good characters in the newest one.
I haven't heard much of the music from recent games, but I have no problem with what I've heard of the music from 10 and backwards. 12's isn't too bad, although I'd like to hear the ending overture (when I actually get around to finishing it...) before I judge the soundtrack overall. I would just like to see a return of the beautiful music. :3