he was just plain angry that he managed to lose to obi-wan. when he knew he was a better fighter a more agile opponent who was more powerful than anyone could ever imagine he was told for years by the jedi council.
Darth Vader showed no emotion at all when he killed Obi-Wan Kenobi. If you watch the scene carefully, you will see Kenobi pausing. He was letting Vader kill him. Whether Vader knew this at the time, or discovered it later, is an open question.
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.
Darth Vader didn't know about this particular skill because it was a practice that was long forgotten and was rediscovered by Qui-Gon Jinn. Given this, the Sith Lord couldn't believe that Obi-Wan vanished when he died — perhaps, even dubious at first about whether or not he's really gone.
Anakin admits to Obi-Wan that he has been arrogant and unappreciative of his training, and apologizes to his master. Obi-Wan assures Anakin that he is proud of him, telling him that he has become a "far greater Jedi than I could ever hope to be."
He slays Sidious and returns to Obi-Wan, begging for atonement by execution, only to be met with true forgiveness instead. But just as this fantasy Obi-Wan refuses to strike his former friend down, Vader refuses to turn his back on the dark.
Vader responded “I am not your failure, Obi-Wan. You didn't kill Anakin Skywalker. I did.” This allows Obi-Wan to finally accept that Anakin is truly gone and that there was nothing he could have realistically done to save him.
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.
Many have taken to the Internet to suggest that if it was really killing Kenobi that Vader was after, he simply could have brushed away the fire that followed to thwart his escape. And that is true. However, Vader is not just looking to kill Kenobi. He wants to make him suffer.
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.
After the destruction of the Death Star, Darth Vader became obsessed with finding Luke Skywalker.
Sand, obviously sand. You see, the Sandman from Spider-Man was the very reason he and his mother were in slavery, and was the one who sent the Tusken Raiders to kill his mother.
Obi-Wan knew it was only a matter of time. So, he made the difficult decision to use his learnings and become one with the force, rather than let Vader decapitate him.
At the end of Revenge of the Sith, Obi-Wan believed that Anakin was dead. Due to Anakin turning to the dark side, Obi-Wan had to face him in a duel, which ended with Anakin losing most of his limbs and being burned by a river of lava.
Obi-wan regrets are layered. He regrets training Anakin and him regrets failing to train Anakin. He regrets hurting Anakin and he regrets not dying there.
It mostly stemmed from Anakin feeling that he was shown disrespect by the Jedi High Council when it wouldn't promote or trust him as much as he believed they should. This condescension is something Anakin often voiced to Padme Amidala, who would oftentimes offer him consolation.
On Obi-Wan Kenobi, Darth Vader had been operating for ten years, making him 32 years old when he encountered his old Master, who had been hiding since Order 66. The pair fought twice, but it was during their second clash that Vader uttered a harsh truth.
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.
This is confirmed later in the movie when Obi-Wan informs Padme that Anakin killed them. Both are torn apart with hurt and confusion, trying to make sense of something so terrible.
The short answer is yes, without a doubt, Vader regretted becoming a cybernetic monstrosity. First, there's the constant pain and discomfort from his suit. Worse, however, is the psychological pain. Vader destroyed everything he had ever known for a chance to save Padme.
After defeating Darth Vader in the Obi-Wan Kenobi finale, Obi-Wan broke down and began tearing up when he saw Anakin's scars. It was the first time he had seen Anakin's face since leaving him to burn on Mustafar, and so he apologized for everything that had happened.
For years, Vader hated Obi-Wan, having been struck down by his mentor and left for dead while also believing the Jedi had worked to turn his true love Padmé against him.
Obi-Wan Kenobi has provided context for Obi-Wan's failures as a Jedi Master. He failed Anakin by being more of a friend than a mentor. His fears and insecurities held him back, despite having obvious proof that Anakin was a danger to himself.