Mystery Dungeon: Shiren the Wanderer is a sublime example of the roguelike genre. Unfortunately, that means its probably going to turn off more people than it will turn on. Shiren takes no prisoners and demands that you rely on your own wits rather than an endless slog of level griding. It's a title which reminds you that games are supposed to be about the journey, and not the destination.
Learning to play the game well is such a rewarding experience in and of itself that completing dungeons simply becomes the icing on the cake. It may not be a game for everyone, but those that can truly immerse themselves in Shiren the Wanderer will discover one of the most enjoyable experiences the DS has to offer.