I think Luke and Vader should have remained on the death star. Done the whole saving, reconciliation thing right there in the throne room. It would have been tragic, but not dark. Tragic in a fulfilling sort of way. Vader had obviously fulfilled his destiny, to have that the fulfillment of Luke's destiny as well would have upped the ante.
I understand that wasn't the tone they were looking for, but it would have been a "bold move" that lucas likes so much.