Question: After Anakin becomes Darth Vader, he seems ruthless, actually evil. "From my point of view, the Jedi are evil!" Is just one quote. That being the case, this movie makes it seem like Anakin knows that he's evil and wishes he wasn't. Basically, my question is, why didn't Anakin turn on Palpatine sooner? Or simply leave the Sith?
Answer: Anakin was seduced by the emperor to think that the Jedi were evil. This was partly fueled by anger &fear, thinking Padme would die if Palpatine didn't help save her. After he turned to Darth Vader & joined the dark side, he eventually realised the true nature of the Emperor, but he was to weak to do anything about it. Darth Vader still wanted to rule the galaxy, but didn't want the emperor controlling everything. He just wanted to use Luke to help overthrow the emperor and take over the galaxy. It wasn't until he found out he had a daughter also, and saw Luke about to die by the hands of the emperor, that he realised that Luke was right & he needed to switch sides.
Vader was not just using Luke to kill the Emperor. He actually did want to rule the galaxy as father and son - if Luke would turn to the Dark Side, that is.
Answer: Darth: "Obi-Wan once thought as you do. You don't know the power of the dark side. I must obey my master." It's implied that the dark side is intoxicating, once you totally give in to the dark side it has a hold on you, and appeals to morality and rationalization are useless against your lust for its power. (On a symbolic level, the dark side is a metaphor for vice. Darth Vader is an addict and abusive parent. It's actually funny how many scenes still make sense if you replace "the dark side" with "the bottle" or similar).
TonyPH
If we bring the prequels into it, it's one of the criticisms of those films that they only make the question of how much Anakin is a "true believer" more confusing. But it stands to reason that at first Anakin may feel vindicated in his resentment toward the Jedi. Later on, Vader may not feel that as strongly, but by then his anger has turned toward himself for failing to save Padme. He may feel that a man as terrible as he does not deserve to be "rescued" from the dark side, leading to a feedback loop where he only gets further enamored with its power and does more evil things which causes him to hate himself even more, and so it goes.
TonyPH