Anakin Skywalker/Darth Vader's fundamental weakness is that he was never really a believer in the Dark Side, or in the Sith, or the Empire. He was conned, all the way along. He thought tinkering with the Dark Side could help people he loved. Palpatine/Sidious merely leveraged his fear at losing Padme to stoke this.
Even after his brutal scorching in the fires of Mustafar, sand remained the only natural phenomenon that Vader feared. To him, sand was a reminder that he'd failed to save his mother or Padme from death.
In Star Wars Canon, only Luke Skywalker can be acknowledged as the one who truly defeated Darth Vader.
Darth Vader hated what the Death Star stood for, and maybe if Palpatine took his qualms a bit more seriously, it would still be around to help them to rule the galaxy to this day.
The first two episodes of Obi-Wan Kenobi are a master class on how the Sith's biggest weakness continues to hamper them no matter when they appear on the timeline. The Sith's desire to dominate and control means they don't have real friends or allies.
There has been no Sith, as powerful, meticulous, nor as evil as the Emperor himself, Darth Sidious. As previously mentioned, Sidious trained in the Dark Side by Darth Plagueis before Sidious killed Plagueis in his sleep, making Sidious a Sith Master.
Jedi and Sith alike fear the loss of power, but the Sith choose to harness that fear as a source of strength.
After the destruction of the Death Star, Darth Vader became obsessed with finding Luke Skywalker.
Anakin does not have even the slightest bit of remorse. By the end, he feels nothing but anger. Although he feels regret for killing Padme, he still helps the evil Emperor. The film ends with Anakins standing side by side with the man on whose behalf he has committed all his crimes.
The added risk Darth Vader takes in allowing children to live in a situation where he could have killed them proves that he regrets killing Younglings and will avoid harming any more children for the rest of his days, though intense intimidation is a dark strategy to avoid repeating his Youngling massacre.
Because he was not an active member of the Jedi Order during Order 66, Infil'a escaped execution. Some time later, he faced the Sith Lord Darth Vader. Infil'a put up a fierce fight against Vader, almost killing him by throwing the already damaged Sith Lord off of a cliff.
However, once Luke fully embraced his power in Star Wars: Return of the Jedi, he proved that he was indeed stronger than Darth Vader and struck his father down.
Master Yoda has risen above all others to claim the top spot as the most powerful Jedi of all time and the true chosen one according to IGN's audience. He won pretty handily as well, as he was victorious in 89,756 of his 95,243 battles and had a win percentage of 94.2%.
Yes, he did. In Revenge of the Sith, Darth Vader cried because he realized that the woman he loves, Padme, doesn't “love” Vader, but rather she loves the good person, the hero of the galaxy, Anakin Skywalker. Anakin felt deep guilt, but that guilt was not enough to stop him.
Darth Vader died after being weakened due to to a lighstaber duel with Luke, where Luke managed to knock him down and cut off one of his hands.
Obi-Wan is forced to turn a light on when he is confronted with Vader, and not only because he's frozen with fear in the specter of death. This is the monstrous form of his failure and his hubris. This is the brother he once loved, and the “chosen one” hope of the Jedi.
As he turned to the Dark Side and became Darth Vader, Anakin came to hate Obi-Wan, but never stopped respecting him. In the end, it was Vader who would take Obi-Wan's life, but it was Obi-Wan who would set up the path for Anakin to be redeemed.
What Padmé knew about Anakin's previous dark deeds. Padmé was well aware that Anakin had committed dark crimes that would've started his fall to the dark side. He even confessed to her that he had massacred an entire Tusken Raider village to avenge his mother, leaving no one alive.
Yes, when Darth Vader turned back to Anakin Skywalker and sacrifice himself to save his son, he dies and Obi-Wan uses the force to connect with Anakin's spirit. In that time Anakin apologizes to Obi-Wan, desperately asking him to forgive him for everything he has done to him and everybody over the years.
Grand Moff Tarkin. Although his status in the Empire may rival or even surpass Vader's own, Vader nonetheless respected Tarkin a lot, for many reasons. He thought Tarkin as one of the more competent and dedicated Imperial officers, with a sense of honor and being able to inspire loyalty in his subordinates.
He could perform incredibly powerful Force Pushes and Grips, and was capable of breaking through the defenses of Force-Sensitive individuals. Vader was also adept at saber throw, which he would often utilize in combat to make up for his relative lack of mobility.
Tulak Hord. An emperor of the early Sith Empire, Tulak Hord was an unrivaled force wielder and dualist. Known by many as the 'Lord of Hate' and 'Master of the Gathering Darkness'.
As powerful as Darth Sidious may have been, it's easy to forget he actually seemed afraid of Master Yoda. As seen in Revenge of the Sith, Palpatine initially thought he could deal with the aged Jedi Master - and then, when Yoda proved able to counter the Sith Lord's Force lightning, he fled.