Considering the difficult relationship between Obi-Wan Kenobi and Darth Vader (Hayden Christensen, voiced by James Earl Jones), it's no surprise that a big chunk of the finale is dedicated to a massive encounter between the two. The former master and apprentice begin an epic lightsaber battle just 15 minutes into the episode, and it only gets more awesome from there. Vader's absurdly strong Force telekinesis is on full display, and while he doesn't explicitly show it, the moment he finally gets the high ground must be a pretty cathartic experience. Obi-Wan takes a bit more time to get his Force engine going, but when he does, Vader finds out the hard way that he's not the only Force user who can throw massive objects around.
When Obi-Wan finally manages to incapacitate Vader and slice his helmet open, the physical battle turns into a war of words. This may just be the most damaging part of the duel for both parties, as Obi-Wan tearfully apologizes for Mustafar, while Vader denounces his former identity. The Jedi gets the message. "Goodbye, Darth," Obi-Wan utters with sadness, making clear that he now feels that his former apprentice no longer exists. Vader is left in the desert, screaming his opponent's name in vain. Hey, not everyone can have a happy ending.
As a viewing experience, the entire meeting is thrilling. It finally shows the audience a bit of Christensen's Vader face and, thanks to the broken mask, mixes Anakin's normal voice and Jones' booming Darth Vader voice into a chilling mish-mash. Lore-wise, the exchange is also pretty important. After all, it explains why "A New Hope"-era Obi-Wan keeps Vader's identity secret from Luke, and insists on calling his former apprentice by his Sith name even when they're alone. For him, Anakin Skywalker truly doesn't exist anymore.
