Usotsuki Mi-kun to Kowareta Ma-chan Totteoki no Uso is an amazing psychological manga about troubled children scarred by their experiences of kidnapping and murder.
Story - The story is excellent, full of twists and turns and very fast paced. Not much to say without spoiling too much.
Art - Decent, clear art. What more can you ask for?
Characters - The characters make the story, they are all interesting and you learn a little about all of them, but in true suspense manga style, not everything about all of them. You learn the motives, you learn who did it, you learn to love the manga for a simple psychological horror.
Overall - This has been a short review because revealing too much would be spoiling it, read it, it's not that long.