Thought I posted about this before, but I couldn't find it if I did. Anyway...
It may sound queer, but I picked up this game today and I absolutely love it. A real breath of fresh air. Basically, it's a collection of brain teasers like you find often on DS now, but instead of just being this sterile collection, it's got a nice creative packaged that comes with it, too. So you've got a story with strange, interesting characters, some phenomenal art, fully voiced cutscenes, some minigames and side stuff, and all kinds of other little odds and ends. If you're looking for a puzzle game that fits the riddler/brain teaser mold but actually offers you a reason to keep coming back beyond the raw activity itself, you should really try this out. Don't be fooled by the kiddy look, it's not actually as kiddy as it seems looks-wise, and it's got a pretty decent story and some very tough puzzles kids would be hard pressed to figure out.