I've read Stephen Rebello's non-fiction book Alfred Hitchcock "The Making of Psycho" where this movie is based on and it's positively brilliant. And Scarlett Johanssen plays the Janet Leigh role.
The movie is supposed to be a behind-the-scenes look at how Hitchcock made PSYCHO. The circumstances that led Hitchcock to buy the film rights of the bestselling novel from Robert Bloch, the wild ride during production (and the tricks they used for the shower scene, the death scene of Martin Balsam's character and the ending), Hitchcock's manipulation of the censors to have the movie shown without cuts and how it was marketed during the Sixties.