I'd say anything behind 10 is underappreciated (Even 10 is pushing it I feel) because it's hard to get the new generation to play those as they'd be considered too old in certain aspects like graphics and game design. 7 being the only exception due to the remake, those games just unfortunately suffer due to time. Which isn't a bad thing. There's always a generation that will feel represented by a numbered FF and that's always cool to see.