RPGs today seem to focus around stat managing. Then it splits to either Western RPG, which normally concentrates on doing whatever, and then there's the JP RPG, which is rather linear.
Castlevania: DoS has elements of RPG, Action, and Adventure. However, I wouldn't really recommend it to someone if they just beat FF7. >_>
Anyway, the DS is certainly worth it. If all you care about is Final Fantasy, you have 6 numbered Final Fantasy games and FFTA. Xenosaga Episodes 1 + 2 are on the way, and so is a sequel to Final Fantasy: Crystal Chronicles. Then there's Mario & Luigi: SuperStar Saga and Mario & Luigi: Partners in Time. Then there's the Golden Sun games and Tactics Ogre. o_O You really can't go wrong when it comes to RPG's with the DS/GBA. And in other Genres, ithey certainly appeal. The Castlevania Games have a great balance of action, adventure, and RPG like Stat Managing. The Super Mario games are "teh awesomez". Mario Kart DS is easily one of the best Kart Racing games ever. And much, much more!
DS/GBA = God. >_>