I know this has been recommended already, but I just finished
Trace Memory (Another Code), and I absolutely loved it! Yes, it's on the short side (I clocked 7.5 hours), but it is a truly delightful game. The puzzles, while being pretty straightforward, are fun to do because of the use of the DS functions. I'm going to replay it because there are puzzles I didn't do that aren't necessarily important to finish the game (but do contribute to the story) and I know that I didn't find all of the inventory I could have.
Well worth getting.