Few may know about this excellent series, but Etrian Odyssey is one of the most unique games I've played on the DS.
It combines old school dungeon exploration with picturesque graphics from the DS. ((Some may complain about the anime style of the character design, but I don't mind))
The plot is to explore a labyrinth using the town as your home base. You create a party from many different classes of adventurers and you quest into the dungeon. A stand-out feature is you have to draw your own map! Including walls, doors, traps, chests and many more using the touch screen.
I currently own Etrian Odyssey 2 which I consider to be one of my favorite DS games, in which you scale up a labyrinth on the inside of a tree. The next installment of the game will feature an underwater labyrinth and all new character classes.
One warning, the learning curve in Etrian Odyssey starts off steep. VERY steep. As you start you will find that you will die. You will die often. The game is unforgiving but as you learn how to stay alive you will be able to explore with greater ease. Yet even veteran explorers still manage to succumb to the terrors lurking in the Labyrinth.
Did I mention its very fun? I can't wait till the third one comes out. Which will be soon