Alfred Hitchcock's Psycho is a stellar example of art in horror movies. Taking the viewer on a seemingly nonchalant trip with a woman who just committed a crime (which in its self doesn't sit right), the story suddenly turns in a WHAT THE?! nail-biting roller coaster.
I actually have no other words for it. This movie has already been covered in writing classes, movie classes, bar room debates, and likely on a television set somewhere every Halloween. Why? Because it is that good.