Puzzle games:
Meteos
Tetris DS
Puyo Pop Fever (hard to find nowadays, but good!)
Brain Age (for the sudoku)
I’ve heard good things abouit Prism: Light the Way and Puzzle Quest, but I can’t verify as I haven’t played them.
RPGs:
Lunar Knights
FFIII (according to my brother, anyway)
Pokemon Diamond/Pearl
grab some oldies from the GBA library - FFIV (even though a DS remake will be out shortly), Fire Emblem, Tactics Ogre, Riviera, etc.
You can also check out the recently released FFXII: Revenant Wings and the Dragon Quest Monsters game, although these are probably of a different breed then what you’re looking for…
Adventure:
Phoenix Wright 1-3
HOTEL DUSK (still my favorite game I’ve played all year!)
Zelda: Phantom Hourglass is probably a solid bet, but I haven’t played it yet, either…
I’m sure there’s many more I forgot, but those should do the trick
