Star Wars: Episode 3
Not going to say much because I dont want to ruin anything, you know that Skywalker turns to the dark side. All and all, good acting from everyone save Natalie Portman. She was unbearable no matter how hot the actress was, her acting is awful in this movie. However every other part got played to perfection.
Go see it, and if you can, watch that Clone Wars cartoon before seeing it. There's a few little bits in that you'll appreciate if you've seen the cartoon.
9/10 (I can just pretend there's only a trilogy anymore, however I still refuse to recognize the first two terrible films).