I think it really improved some key moments, and some interesting quotes. Primarily the last scenes in ROTJ, when the emperor was force lightninging Luke, you really know what Vader is seeing. And in that moment, you know that he is seeing the dark side for what it truly is. He finally realizes that the dark side doesnt lead to protecting those you love, but it leads only to destruction and death. And the moment when he takes the mask off, you know that he truly understands what it means to protect the ones you love, and that it has nothing to do with manipulating midichlorians.
Also a lot of quotes gained more meaning, like when Yoda says "Don't underestimate the power of the emperor, or suffer your father's fate, you will." Now we know he is the expert on underestimating the emperor.
Yeah, you'd think the Emperor had come back to life or something.