If 'all you care about' is Final Fantasy, then the DS is an excellent system to broaden your horizons. There's a pretty high chance of you picking out a high quality game at random, though there are a few stinkers as well.

There are several recent topics with people asking what games to get for the DS. The ones that show up frequently are all good picks.

Castlevania is an action game with RPG elements (EXP, leveling up, getting stronger and such), but there are a few other RPGs I'm looking forward to as well. There's Magical Starsign, which you can play with 5 more people over the internet I believe. Pokemon Diamond/Pearl, which will have online battles among other features. Children of Mana and Contact are also 2 RPGs I'm highly anticipating.

I'm not sure if Dragon Quest's Rocket Slime is an RPG, but I'm anticipating that one as well.