DS RPG: If you like strategy-style games, you have Final Fantasy Tactics A2, which is good fun, but somewhat easy, I think, also, the law system can be frustrating. On the plus side, it's less exploitable than in TA. Disgaea is good if you can stand the grind, and even if not, the story is fun enough that giving it at least a try. Devil Survivor
is also fun, although I think the game requires you to grind, but secretly hates you for it, interesting concept too.
On the topic of more traditional RPGs, Strange Journey
appears to be good thus far, but I haven't really gotten too far into it.