I have several extensive Star Wars books, that go into the making of the first six films. Admittedly, I haven't read that much yet, but that's because I have a tough time slowing my mind down to focus properly.
Anyway though, from the little I remember, Lucas' overall intentions for the original trilogy went through many different iterations, between his first outline in 1973 and the release of A New Hope four years later. The only real constant in the whole thing, according to Lucas, was the main trio of Anakin and his two kids, versus the evil Empire. A lot of his early writings weren't even known about by most people, until the prequels were made. His response to people hating on him for making Vader more sympathetic, was pointing out the fact that he didn't have the time or resources to portray certain events the way he originally wanted to.