http://ds.ign.com/articles/804/804448p1.html
Control and gunplay in Dementium uses the touchscreen as a mouse button, and worked really well. When you need to act and aim, the touchscreen works as your cursor, but the game is also filled with puzzles, most of which are simply interacted with via a context-sensitive action button at the top of the screen. At the corners of the screen are access to a map and your notepad. The notepad is a nice addition, as it uses the Nintendo DS screen (like Hotel Dusk) to allow you to write down passcodes and game notes important for puzzles. (You can also doodle and wipe it off later with an eraser.) The game's story will evolve with communication with NPCs (including possibly the woman whisked away by the evil It in the beginning of the game.)