There were lots of unused conceptual artworks for Vader's look in ANH that would have looked great in RotS. The major flaw I now see in the prequels is, that it mainly should have been told within four movies - or three films of three hour length. What people wanted to see is not only the fall of Anakin - but also the "revenge of the sith", who returns reborn out of his own ashes to avenge his fate in blind anger (much like in the sand people slaying scene).
I would have liked to learn more about the heritage of Vader's armor. I remember that the armor had some sort of historical background within the starwars universe, that was more sophisticated than what was introduced in the prequel era. As far as I recall the "Sith" were supposed to be some kind of alien race or culture (much like the mandalorians) and that the title "Darth Vader, Dark Lord of the Sith (tm)" was unique to Vader - a title he gave himself - not Palpatine.
How do you guys feel about this?