Last thursday.
I lost my savestate and had to start again, but even then it was worth it. It's amazing. It's a story where you are dying to find out about the ending. And the ending is awesome. The combination of puzzles, amazing and cute cut-scenes, the atmosphere of the game and the Professor's BRITISHNESS just make this a real (and overseen) gem in DS' game-gallery.
I also like the game for not being one of those games that try just too hard to use the touchpad. Like when you play a game and you'd be fine with simply using the buttons and it's fun and all, and then you have to use the touchpad for no apparent reason.
This game didn't have that, and while that's not special at all, it was still a bonus to me.
You should definitely give it a try.