This is my fave film of the OT, for one main reason - the unbridled emotional weight between Luke and Vader. Mark and David Prowse both embodied their characters so well, and James Earl Jones' lines just added even more to the intensity. Ian McDiarmid's first entry as Palpatine was so deliciously evil; you could tell he was enjoying the part like crazy.
As for the rest the film, it was pretty good; I even liked the Ewoks. Carrie Fisher would later complain about her infamous slave-girl outfit, comparing it to "something supermodels would wear, in the ninth circle of hell". But on the whole, I think the bulk of the movie still holds up - its a great sendoff for all the main characters, and to be honest I don't think we needed any more sequels following that point.