I would like to see what the story is about, the choices, things of that type honestly. All VNs have nudes and scenes, but how they tell the story is what sets the writers apart. Sometimes you have a phone that gives you relationship information, progress, and other hints. Sometimes you just mash away at the space bar and have no choices other than inside or outside, if even that. So I want to know how interactive the game is. A demo usually supplies those mechanics.