It's commonly claimed that the reason the original Star Wars films were so much better than the prequels was the work of Marcia Lucas in the editing suite.
These accounts about Marcia are deserved but downplay the contributions of Paul Hirsch and Richard Chew. The three of them absolutely saved Star Wars in the editing room.
The lack of Lawrence Kasdan is the reason that every piece of dialogue in the prequels is incredibly awkward (but apparently extremely meme-able).