You make a VERY interesting point though.....I think it would have been genius to have never explained who Vader was in the prequel. Maybe have us believe that Anakin died during the fight with Obi-Wan and then just have this new apprentice, Vader show up and start helping the Emperor whoop Jedi ass.
There's quite a few directions to go in. Some bring up some serious continuity errors....but given some talented creativity, Lucas could have come up with something really ingenious.....instead he seemed to take the easy and lazy right which was to write them as prequels and make it all one big story. He should have stuck to what the press "created"....those three trilogies that were all separate stories, but slightly interconnected.
I think the biggest mistake was to shift the focus to Anakin. That was retarded to the extreme. The PT should have been about Anakin and the OT was about Luke, plain and simple, cut and dry.