Star Wars '77 was the soup that your mom made once by starting with grandma's recipe, then throwing new things into the pot without measuring them. The result was absolutely, unexpectedly delicious and completely satisfying on its own.
ESB was your mom's attempt to replicate that soup by laboriously measuring each ingredient and tasting it at every turn, while grandma hovered around wondering what was wrong with her old recipe. It was only supposed to be basic vegetable beef soup, after all. The taste was more subtle, more delicious, more simmered in sauce than before, but the initial delight of discovery was gone, never to be recaptured. It also seemed incomplete on its own; it left you wanting more.
ROTJ was the soup as grandma made it, simply wanting her old vegetable beef soup again. Mom tried to add what made it special, but the results were confused, conflicting.
The prequels came about when grandma got too old and tired to care about using good ingredients, and instead made do with cans of Campbell's soup while hoping nobody would notice.