The July 1997 issue of Playboy has an interview with GL where he said:
"When the story of the six films is put together, it has a more interesting arc because you're actually rooting more for Darth Vader than you are for Luke. Until now, you didn't know what the problem really was, because Darth Vader is just this bad guy. You didn't realize he's actually got a problem too."
I don't know what this means, but I thought I would post it. Any theories?