The rushed ending ruined it for me.
Graphics - a-ha should be proud. The pencil sketch, "Take On Me" character models are great. And the dark, muddy environments really make you feel you're in a mystery novel.
Sound - The majority of the sound comes from the in-game music. It makes you feel you're doing something bad in the back of a dark alley, but if you're looking for it to scare you you'll be disappointed. Other sound effects (doors opening/closing, etc.) are well-done and don't sound tinny at all.
Controls - Hold the DS like a book, move using the touch screen and click on the screen for an action. Touch-screen controls work better than "The Legend of Zelda: Phantom Hourglass," probably because not all the action is limited to that one screen.
Gameplay - Other than the rushed ending, the game is a lot of fun if it fits what you're into. If you don't like slow-moving, text-based games, don't pick it up. You'll be severely disappointed.
Overall - Not much else to say that hasn't been said yet.