One great 'Star Wars Darth Vader Fanfic' is 'Vader's Redemption'. It shows a different side of Vader, exploring his inner conflict in a very engaging way.
I really like the fanfic 'Darth Vader: The Hidden Years'. This one delves into the time period between Episode III and IV, when Vader was still adjusting to his new life as a Sith. It gives a lot of backstory and character development that you don't get in the movies. It shows how he's dealing with his new powers and his relationship with the Emperor.
One great fanfic could be 'The Redemption of Vader and the Ascent of Luke'. It delves deep into the relationship between the two. It shows how Luke's unwavering belief in the good in Vader starts to chip away at Vader's dark side. It's filled with intense lightsaber battles and emotional dialogues that really capture the essence of their connection in the Star Wars universe.
A good 'Star Wars Darth Vader Fanfic' should have a deep understanding of the character. For example, it should explore Vader's duality - his past as Anakin and his current state as Vader. Also, it should fit well within the Star Wars universe in terms of the lore and the technology.
Darth Vader was once Anakin Skywalker, a Jedi with great potential. But he was lured to the dark side by Palpatine. He became a Sith Lord. Vader was a fearsome figure in a black suit with a red lightsaber. He carried out the Emperor's evil commands, like hunting down Jedi. However, in the end, he redeemed himself by saving his son, Luke Skywalker, from the Emperor's wrath at the cost of his own life.
Darth Vader was once Anakin Skywalker, a Jedi with great potential. He was lured to the dark side by Palpatine. His fall was tragic. He became a Sith Lord, a powerful enforcer for the Empire. He wore the iconic black suit and had a menacing presence. He was involved in many battles, like the destruction of Alderaan. In the end, he redeemed himself by saving his son, Luke Skywalker.
A good fanfic about Luke and Darth Vader should first and foremost have a strong understanding of the characters. They need to stay true to their personalities as seen in the movies. For example, Vader's internal struggle between the light and dark side should be well - represented. Also, a great plot that ties into the existing Star Wars mythology is important. Maybe it could involve a new threat that forces Luke and Vader to work together, or explore their relationship in a different time period.
He might be shocked by the advanced technology. The Empire's weaponry would seem primitive compared to future tech. He could also be intrigued by the new forms of the Force if they had evolved.