Phoenix Wright Surviving High School Cause of Death Unfortunately, there aren't many good visual novels on the appstore that aren't horribly written/translated.
Try Higurashi When They Cry (episode 1 is free) Its more a sound novel then a visual novel. I didn't expect much from this, but was really supprised. It's very entertaining and exciting. The story starts really slow, but picks up after a few chapters. It has a lot of plot twists and gets pretty gruesome and disturbing halfway through. Like i said episode 1 (of 4) is free, so try it and see if you like it.