The moment when the franchise ended in the 1980s. It was really principled of them to stop making these movies on a high note, rather than allow the series to devolve into half a dozen cash-grab pieces of trash beloved only by neckbeards and submoronic mouth-breathers.
I would not call Return of the Jedi a high note.
Why not?
I guess it's a matter of opinion, but I don't think it's a good movie.
ROTJ is a very schizophrenic film. As mentioned above, the Luke/Vader/Emperor plot is absolutely brilliant and the perfect climax and resolution to the original trilogy. Unfortunately they had no idea what to do with the rest of the characters so everything in the other half of the movie on Endor is terrible - even the Han-Leia dialogue is uncharacteristically poor for the OT, foreshadowing the disaster that was the prequels.