And has been said, i am sure it was never Vader's story from the start,he was just the villian to begin with, you can tell that it was about Luke etc and George changed his mind to make it Vader's story.
Though the Prequel story is good and George said "it would be rather boring", Sith is the only official prequel for me that I find entertaining, the others are so boring, may he is right they are supposed to be, The only way I have now found the other two to be entertaining is watching the fan-edited versions of them two Prequels(which by the way does turn TPM into a much better film by ditching the crap, and they thankfully do get rid of the horrendous love dialouge in Clones to make it less painful and in turn better and both less dry)at least the originals were entertaining all the time (to me) while having a story, and for me part of the reason I watch Star Wars movies is to be entertained, if I want to watch something boring I will watch two hours of some foreign arthouse film .