If it were any other genre, the finale of The Empire Strikes Back would be sitting pretty at the top of the list. After the unexpected success of Star Wars, George Lucas still had plenty to prove, but the necessarily downbeat ending planned for Empire was hardly the stuff of blockbuster cinema. It seems impossible now, but back then the audience would have needed a reason to return for the third film. Darth Vader’s revelation that he is Luke’s father was exactly that. It’s a classic soap-opera cliffhanger.