Roguelikes, specifically the Mystery Dungeon variety of the kind made by Chunsoft (and roguelikes made in the style of Chunsoft's Mystery Dungeon game), are booming. The list currently includes three DS Pokémon Mystery Dungeon games, two Izunas, Shiren the Wanderer, Tao's Adventure, and homebrew games including Powder and Nethack. That's a lot of random dungeons.
Roguelikes are a very strange genre: death as an essential part of gameplay, and extreme difficulty in general, are unusual for the DS, and things like random dungeons seem archaic at first. If you've gotten into one of these, were you always a Mystery Dungeon fan? Or did the explosion of Mystery Dungeon games on the DS get you interested?