Well the problem is Vader is irrelevant. One could easily write him out of the stories and little would be lost. He was never fleshed out, nor given the proper dark foreboding of a true monster. It wasn't till later people started adding things to explain him, often with several versions depending on what the person wanted. A ruthless villein, a misunderstood lover boy, a duty bound father, and much more.
While I like these new explanations, like the bad ass one, I have to admit it is forced and painfully re-conned to the point of needing a reboot.
A bigger problem is the the force. They need to make two very important definitive decisions. Is the force black and white or is there gray? They have since answered this with the introduction of some minor characters who are gray, but avoid it far to much. Does the idea of taint exist? That is to say if one learns sith powers do they become corrupted regardless of their original vitreousness, the Jedi order keep saying this is the case but it could just be a lie or bad info.
It is a classic problem with magic, if you give it too many rules then it is not magical, but if you make it too vague then it seems like you are just making things up and can't write a good story.