Star Wars: Episode V - The Empire Strikes Back

The 'best' Star Wars film, where Jedi Master Yoda was introduced to the world. Add in the great opening battle on the ice planet Hoth, and the earth-shattering secret that Darth Vader tells our Luke in the depths of Cloud City, and you've got yourself a mega sci-fi classic that ends with one hell of a cliffhanger. Space opera has never been bettered.