I never really understood that the prequels were so highly criticized. I mean, yeah they weren't exactly masterpieces, but neither were the originals.
I think you are overlooking the point that the originals were kind of groundbreaking in being big SF movies, which created a cult following and the accompanying (western) worldwide merchandise which helped boosting the iconic nature of the different characters in the movie. I think nothing like that had happened before when Star Wars came out. The impact on popular culture was pretty huge so to say, which stands aside of the depth of the storyline. I think still today, the image of Darth Vader, besides Hitler, is pictured as being pure evil, according to several polls.
BTW: Even a large anti USSR project I came up with during the eighties, was named after this movie
