I always liked Hotel Dusk: Room 215. I bought my original DS, that got lost, because of it. 
 
It is such an original and well made game, unique in the repertoire or the Nintendo DS. It has a convoluted and interesting story, simple yet good artwork, and functional gameplay.  
 
The game sometimes due to the long winded experience it provides, sometimes got stale on me, still interesting enough to finish it.  Still I've got to say I was disappointed about the ending. The story never really wrapped up, and the characters whose key for solving the mystery never really materialize in the story. It was bad, as it seemed to shamelessly wave at a sequel to give a proper conclusion to the story. 
 
In the end, t is a great game, but disappointing as time passes by.