Undoubtedly most powerful character transformation in this movie will be Anakin's fall to Dark Side. He has already taken first steps in Episode II, his impatience and arrogance playing primary roles in this foreshadowing. Almost certainly Anakin and Obi-Wan will have to confront each other, likely resulting in a fight of some kind. A lightsaber battle between these two would be interesting to see, as of course both now other's style and technique. Each would have another advantage, as well: Anakin can fully use power of Dark Side to aid him, if he's that far along yet; and Obi-Wan has more experience and seems somewhat capable of protecting himself from such powers, ala blocking Dooku's lightning attack. Since we know both must survive encounter to be in Episode IV, it would probably then end either by stalemate, distraction accompanied by one fleeing, or apparent death, such as falling off of a cliff. Also, we must realize that Vader, as seen in Episode IV, is in his life-support armor, so it is possible this fight is how he sustains those injuries.

Another hugely important facet of story is downfall of Jedi. We have already seen their numbers drop in Episode II during Geonosis battle. If Clone Wars are still in full swing during Episode III, more will be falling in this movie, as well. Yoda and Obi-Wan Kenobi obviously survive, so they must somehow escape conflict in order to set themselves up for Trilogy. Since Mace Windu is not mentioned in Episodes IV-VI, it can be assumed that he will die or his fate will be sealed in Revenge, as it would be incredibly cheap of Lucas to just say "Oh, well, he died somewhere in gap, but I'm not going to tell you how." Mace is one heck of a fighter, so either his death will be spectacularly planned, or else he will have to sacrifice himself to save others (or just one other).