Gameplay comes first. Always. Otherwise, it wouldn't be very much of a game, now would it? Difficulty falls under this category; a game has to have balance between its hard and difficult parts. If it's hard, they have to give us the means to beat it, then let us bang our heads while we figure it out.

Story comes second. Graphics is dead last. Shiny objects are not the best objects.

However, I've found that for FFs, plot comes first. Mostly because for every game after FFVI, I've been expecting what is basically a visual novel; interaction for the sake of the plot, not because it provides anything new or revolutionary.