No, 4-6 were good popcorn movies. They weren't high art by any means, but they were far better than the Prequels which were trash. The reason is simple: in 4-6, other people were able to cover for George's inability. The prequels suffered for bad direction and horrible dialog (/script). In 4, his (now ex-)wife edited the script. If it weren't for her, 4 would have the same utterly horrible dialog as the prequels, and 5 and 6 might not have happened. George was also a better director back then, because his ego wasn't as big. 5 was great because it had different writers (Brackett/Kasdan) and a different director (Kershner). 6 was OK because it too had a different writer (Kasdan/Lucas) and a different director (Marquand).
With the Prequels, Lucas did everything, and no one wanted to say anything to him because his ego was so big and he had put himself in charge of everything, so the results are predictably bad. Lucas was never much good at writing a script or even directing actors, but he refuses to admit it.