Actually, each Final Fantasy game is a completely different story. FFX is one of the most unique stories I've ever seen in an RPG. It's about love, family, acceptance, guilt, original sin, death, cycles, etc.
You're missing out on good stories that allow you freedom of choice, because you prejudge the concept of a jRPG.
I'm not saying Diablo is fun, nor would I consider it a full fledged RPG. I asked what your critera is. Diablo meets most of them.