9. Psycho
If anyone can make a film exceed the quality of the written source material, it is Alfred Hitchcock. Psycho remains revered as one of the greatest horror films of all time, sinister, brooding, Freudian, and of course, boasting one of the most fiendishly barmy twists in film history. Hitchcock deviated from Robert Bloch's source text in a number of ways, chiefly with his depiction of the murderous Norman Bates (played by Anthony Perkins in the film), who in the novel is a rather weaselly, unattractive young man, yet Hitchcock pitches him as a little more suave and sweet, making the ultimate revelation all that more surprising. Furthermore, Hitchcock broke all the rules when he killed Janet Leigh off half an hour into the film, and makes of the iconic shower scene far more than Bloch did in his book; it is a shocking, revealing scene in the film, but it runs scarcely over a page in the book. This is a clear example of a filmmaker making a judgement call against a book and, as is rare, actually being right about it.