Well, in my original rewrite, I obviously went beyond using Vader and Palpatine as the only primary antagonists.

I expanded on Maul's character, moving him away from Lucas "Dark Smithers" persona and putting him in the Sidious role, effectively giving him his own distinct persona. I tried to make him darkly seductively, but I don't know if I succeeded in conveying that well. I was also planning on depicting him as having a brotherly love and devotion to his master, but that, of course, never came to be.

With Grevious, I revamped him completely. I make him a completely organic being, dropped the "General Grevious" moniker for the EU-derived Qymaen jai Sheelal, and gave him the "ANH Vader" role for my Ep. I rewrite; he was this relatively minor character who would keep popping out from time to time to act as a horribly malicious bastard to the innocents around him. I had him blown to bits at the end, and planned to resurrect him in his more familiar cyborg form in the Ep. II rewrite.

I was developing Dooku into the character I wanted him to be in Lucas' PT, an honourable Jedi with good intentions who still manages to fall to the dark side, a sort of Vader precursor if you will. He would have been good friends with Obi-Wan until Qui-Gon died while under his care; at that point Dooku begins to habour resentment toward the younger Jedi, secretly blaming him for his apprentice's death, starting him on his journey down the dark path. I would have shown him lose his faith in the Republic and the Jedi way and followed his progression from Jedi Master to Dark Jedi.

I also planned on bringing the EU character Asajj Ventress into my Ep. III rewrite. I was going to stay true to how she's been portrayed in the EU more-or-less, but I was going to ditch the twin red lightsabers for one blue and one green lightsaber.

As for my new rewrite ... Should I ever get to writing it, I will add the spirits of long-dead Sith Lords into the mix. They will serve as the villains who originally seduce Anakin to the dark side, becoming his first dark masters. Beyond them, though, I don't have any defined big bads in mind, and probably won't be bringing any PT villains into the mix this time around.