I can't say I feel anything in the duel in Empire needs altering, other than minor cosmetic tinkerings. The actual duel itself works just fine.

I also never liked the angry slashing Luke does in Jedi. It's not that I don't like him being angry - after all that's exactly what he's supposed to be - I just think Mark Hamill looks rather unconvincing the way he handles the sabre. In the same way that someone who doesn't smoke might act how they think it looks cool. You can do the moves, but not the style, something like that. Luke could have chopped Vader's arm off with anger AND style, but Mark Hamill doesn't pull it off. (And as much as I think he's a very limited actor, I don't blame him particularly, as Jedi was very poorly directed where virtuall all the actors are concerned).