IMO Episode 5 was the Masterpiece. This is when George had the money to put into it and because he was trying to be so creative, he offloaded a lot of the writing to a professional script writer and also to a great director.
With Ep 4 A New Hope, he was struggling to get it done on budget and in time. It was like a 12 mill dollar film and he was stressed that the effects would not be finished in time. Apparently his director buddies at a preview like Coppola thought he was mad. Only Speilberg said it would be special
And then came ep5. It was Star Wars with the financial backing. It had actors who knew their roles, great script, and it was dark. Plus it had surprises. No silly ewoks :). That film just came together. It can be argued that even John William's best soundtrack came from Ep5. You had the original Star Wars fanfair and Princess Leah's theme and then we got Yoda's theme and the Imperial march. Just legendary. I remember my housemate seeing it for the first time. This is many years after its release. He was blown away.
I see Ep5 as one of the greatest films ever made. It was a sequel that for once really did out do the first film but the first film will always be special because it did things never done before.
Now to Ep7 and beyond. I cried for joy when Lucas said he was just acting as a consultant. It's the best outcome, He has had the rough script for these from the beginning and George is best at formulating a story and being creative. I got a great feeling about this next trilogy. Disney are a natural marriage for this project as long as the director and script writer nail it. They are even adopting a lot more model effects this time and trying to stop the CGI overload - a great indication that this film is not aiming at just pointless gloss.