Grrrr *Hates Fable*
RPGs are few and far between for the X-Box. If your looking for more of a story based one, like FF, your out of luck. I can not think of one single RPG like that for X-Box. What your going to have to go for is more of the free roaming, stat bullding types. Morrowind is the best out there, and really one of the best games X-Box has. Also it's uber cheap, so pick this one up without fear. Most people tend to enjoy Fable, so grab that one I suppose.
Ah, but let us not forget Knights Of The Old Rebublic. KOTOR is a great mix of stat, story, and chossing what you want to do with your guy. But it's linear as hell.
And if you want, count Shenmue II as an RPG, it's great, and has an amazing story. But it's more of an adventure game.