I didn't look at Rondo of Swords reviews before picking it up, and still disliked it. It's possible that the IGN reviewers had the same opinions as me, but moving on... Let me go through my games. Note that these aren't all games in the same vain as those being suggested, but are those I believe to be good DS titles.
TWEWY - Excellent storyline, and the battle system, while not liked by all, definitely is innovative.
Cooking Mama 2 - Mini-game galore. If you have Gamers ADD like me (although you have finished most of the Final Fantasies, so maybe not) this game is definitely worth picking up.
Glory Days 2 - One of the best DS titles of all time. If you don't own this game, go get it. It is basically a 2D Battlefield in which you pilot either a helicopter or a plane. I cannot go on about this game enough.
Jump! Ultimate Stars - If you like Anime at all, this game is a must have. If not, not so much, although you might still get some enjoyment out of it. My advice is to grab a translated copy if you plan on playing it.
WarioWare: Touched! - Another game to relieve my Gamers ADD.
Castlevania: Dawn of Sorrow and Castlevania: Portrait of Ruin - Excellent games. I'd never played ANY of the other Castlevania games (I know, it shames me.) but these games were excellent.
Dragon Quest Heroes: Rocket Slime - I'm serious. I love playing this game. I've played the HELL out of it. It's almost impossible to describe, but it's definitely worth trying. The game looks rather childish, but can be deep.
FFCC - Multiplayer ALONE wins this game a spot. Co-op in RPGs has been seriously overlooked on all platforms for the last few years.
Mario Kart DS - Well, it's Mario Kart. You either love it or you hate it.
Sorry this post was so long. Anyway, if it comes down to the wire, I recommend Glory Days 2. However, all these games mentioned in this thread have their merits. BiChan, I am getting Contact as I write this based on your recommendation ALONE. I played it and didn't enjoy it, but am willing to give it another chance.
EDIT: Forgot to yell at you for not liking Golden Sun. Shame on you.