How a Book Translates on Film: Leonardo DiCaprio

Books go into so much more detail than the movies they're based on, but Leo DiCaprio's portrayal of Jordan Belfort based on The Wolf of Wall Street was great.  In the movie, Leo DiCaprio saves his friend from choking to death.  As a viewer, you can tell he struggles with the decision to save him.  In the novel, Jordan Belfort struggles with the same decision, but the book goes into detail as to why he struggles.  Leo did his thing, though!  I think it's great when a film gets a book right.  Still, it's good to read the book for more insight.  What are some good movies you've seen based on books?