Someone took the Obi Wan/Vader fight from "Star Wars: A New Hope," extended it, and intensified the choreography. They re-shot some of the footage and put Alec Guinness' face on another performer.
You can really see Vader's festering hatred for Kenobi. He fights dirty, using his fists and even a headbutt. The combat is visceral, and frankly, kinda terrifying. You wouldn't want to be anywhere near this.