I have yet to play XIII, but I've never been disappointed in the gameplay of a Final Fantasy game. Characters and story, though, I think they should improve on a bit. Less linear might also be a good idea, because the open-world is something I do miss from the older games. I still think they come up with great designs for most things (monsters, summons, weapons, etc), but I want to see better character designs (both physically and personality-wise), and maybe more focus on relationships (not romantic relationships, but how all the characters relate to each other. You said yourself that you liked how there was some actual conflict between Snow and Lightning in XIII. They should do things like this more often and it will help the characters feel more three-dimensional). I've been slowly losing interest in the franchise since X, but I'm not saying they should go back to how the old games were, either, because I think they are still developing this series in some ways. All in all, I look forward to FF's future.