I just wanted to comment on this, my friend. The point of Darth Vader's story has always been fall and redemption. The idea that he was a good person who became bad and then good again has always been a central theme of Star Wars.
So I'm not sure what you're saying the problem is with Vader's backstory - is it the fact that he wasn't always evil, or is it the fact that when he wasn't evil he wasn't likeable? Because one point I can more or less concede, the other I can't.
Although even Vader's whininess is consistent with the Star Wars story. Remember that Luke was basically a whiney teenager in ANH and ESB, right? When you watch them in numerical order 1-6 (as I have done, that's a hell of an experience) the fact is that Luke's story mirrors Anakin's, so you watch Luke make these stupid decisions and if you put aside your knowledge of how the story comes out, you realize how close Luke came to complete disaster. So Vader's backstory really draws the Luke/Vader conflict more clearly, and when watching 4-6 you keep seeing Luke do these things and you say, "damn, that's just what his Daddy would have done." And thus when Luke shows up wearing black, choking Gammorreans and threatening Jabba the Hutt's life ("Last mistake YOU'LL ever make!") you realize that Luke is not acting as a Jedi should. He's doing dangerous, wicked things.