Get Toki Tori.
Toki Tori is the best puzzle platformer you'll get.
It's pure awesome.
If you enjoy it, and don't rush, completing all the boards could take 40 hours, but 25ish is more likely. And you'll enjoy almost every minute.
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS