I second Zero Escape: Virtue's Last Reward if you're into visual novels and puzzle solving, its the sequel to 9 hours, 9 persons, 9 doors on the DS but you don't need to play 999 to understand Virtue's Last Reward. Pokemon mystery dungeon is also a fun dungeon crawler if you're into those.
I currently spend more time on my DS right now because I picked up Phoenix Wright again and am playing though the last game of the trilogy. I am already looking for other virtual novel type games to play on DS/3DS and 999 sounds great for a start! <3 Will also stalk ebay if someone sells Zero Escape for cheap.