Heroes of Ruin is like Diablo 3 but the OP didn't ever refer specifically to 3DS.
Some other good (though single-player) 3D RPGs for the DS: Golden Sun (VERY good game), Nostalgia, and both Kingdom Hearts games (though I like Re:coded more since I was 18 when the original KH game came out and it reminds me a lot of the original).
A couple of the most interesting RPGs for the DS are not 3D -- Shin Megami Tensei: Devil Survivor is a game that has a very story driven style but a really awesome combat system, especially once you start getting into the second & third day in-game and have access to demon auctions and fusion. It's a bit of a hybrid between strategy RPG, and pet collection. It is in some ways reminiscent of Persona but the combat system is different. However, the story has a lot of dialogue. I hope that doesn't "bore" a person interested in RPG genre.
I'm also a fan of "Contact" which is very unusual, more of an action RPG system, very unique storyline though.
I also recommend 999 which is more of an interactive novel and puzzle game than an RPG, it's one of the only rated "M" games on the DS system because it's a survival horror story with some strong language and situations.