timdiggerm said:

Isn't part of the point of ROTJ that you're supposed to worry about Luke? If you don't, there's no tension in the Emperor's offer.

The problem there, as the film stands, is that past the first few seconds of seeing Luke, there's never any sign that he might turn. He shows up all mysterious and dark, but we quickly see that he's still on the right path and then he goes to Yoda and it's confirmed that he's a goodie. There is no tension in the Emperors offer. The tension comes from wondering if Luke is right and Vader can be saved or if Luke will die doing what he believes is right.

And besides, I wouldn't say that's the point of RotJ, I'd say the point is in returning Vader to the good side and setting things right. Thus Return of the Jedi.