Ok, you've got this rather wrong, though understandably so. Anakin's conversion to the dark side was rather more realistic than believable, but that's because people like to think of evil as something big and obvious and foreign; in reality evil is none of those things. People really become evil for trifling reasons, generally in a slide down a slope padded by lots of small bad reasons for it.
Anakin, like many, noticed his choice only really after he made it, and then thought it irrevocable when it actually was revocable. Indeed, this is almost the point of the last third of RotJ; Luke eventually convinces his father that his decision to be Sith is not permanent.
I don't know where you get the idea that Vader enjoyed being evil; he never seemed happy throughout the entirety of the three original episodes. Vader rather seemed resigned and very heavily task-focused; he was always in the process of accomplishing something (in the later movies obviously at the command of the emperor). Vader didn't enjoy evil; no one really does (except psychopaths, which Vader wasn't).
Lucas, perhaps unconsciously, captured the truth that Evil is not nearly as glamorous as the costumes it wears, and is far easier than anyone would like to believe.
(Incidentally, it's really silly to describe all evil as being rooted in a lack of faith, since God's good doesn't come from his faith, and we're made in his image. Moreover, it's perfectly possible for a selfless love of Padme to lead to evil; have you never heard of the sin of worshiping graven images?)
No, I'm afraid you'll find it is you who are mistaken. About. A Great. Many. Things.
Vader enjoys the hell out of being evil. He loves the fear; he loves the authority; he revels in his power.
"I find your lack of faith disturbing."
His threats to general in charge of building the Death Star. He loves it. He can't get enough of it.
The rest falls under the Space Opera criticism. If you're gonna give me eight hours of film, the conversion has to be more than it was. But part of the problem is this: There is nothing inherently interesting about the character of either Anakin or Padme. Padme is a queen. She is a nice person. She wears funky hair. Anakin's a sulky jock who is made entirely of mydol chloride or something. That's about it.
And while you make a plea for the "banality of evil," in Hannah Arendt's phrasing, Lucas didn't manage that, either.
I do agree, however, that Luke did spend a lot of time explaining he could un-Sith.
Still, it's a great world that the flat characters inhabit.
I guess that's the problem ... the characters are flat, not round, as E.M. Forster wrote. A flat character will never surprise you. And in three movies, neither Padme nor Anakin did anything surprising.