I have no trouble thinking of examples of books that are better than their movie counterparts, but it's hard to find movies that are better than the book. How can a two-hour movie effectively outshine the original? Psycho comes to mind. It's not my favorite movie, but it's better than the book, thanks to Herr Hitchcock.
The author of the book called Psycho was Robert Bloch. He portrayed the role of Norman Bates as a middle-aged man, dominated by his mother. He also based the character on a serial killer named Ed Gein. Imagine Norman Bates as a middle-aged man! Hitchcock wisely made the character younger, thinner, and gave him a full head of hair. If he hadn't been so awkward socially, not to mention a taxidermy aficiando, one might have even thought him handsome. The young Norman Bates made the movie pop. Sure the house was spooky, sure showers became verboten, but because Norman Bates was slightly attractive and likeable, the movie became even scarier. The take-away: People prefer evil to be attractive. The very thought makes me shudder.