Something I've been thinking about since seeing the ROTS teaser trailer is how Lucas has changed the portrayal of Darth Vader throughout the saga.
In ANH, Vader was a thug, the Emperor's buddy who was a non-military advisor to another (possibly bigger) villain of the film: Grand Moff Tarkin. Vader thought and acted for himself, spoke his mind, even engaged Ben Kenobi in trading verbal barbs, but also took orders from Tarkin and was shown to be more ruthless than situations dictated. It was like Vader was a big boy in the Imperial chain of command, but hadn't really become a "made man" yet in the organization.
Vader's portrayal in ESB was fairly different from the previous film, here Vader was shown to be a driving force in the Imperial naval machine and fully in control of the fleet at his disposal, willing to destroy thousands of Imperial lives aboard a Star Destroyer by making it fly into a dangerous asteroid field. Yet this Vader, with his broad sweeping actions, is clearly shown to put everything else aside the moment his master, the Emperor, requests an audience. When the Emperor orders him to destroy that which Vader is looking to find, Luke Skywalker, Vader suggests taking the boy alive in the most subserviant manner we have ever seen him (this has been changed in the DVD versions, but Vader's manipulation there doesn't really impact any changes to this part of the discussion). Once off the Emperor's leash, Vader approaches Luke about destroying his master and taking his place.
However, in ROTJ, Vader's role changes once again, in the first half of the film he is basically there to tell people to do things the way the Emperor wants, then when he and Luke meet up, Vader talks like a zombie, he "must" obey his master, it is "too late" for him to be saved, even James Earl Jones' reading of the character switches to a monotone zombie-like manner. Vader's actions in the throne room don't take advantage of his ambitions he voiced to Luke on Bespin even though it would have been so easy to do so. Vader simply follows singlemindedly towards his path until Luke ultimately defeats him and then is being destroyed by the Emperor. This plays out like Indiana Jones & the Temple of Doom where Indy drinks the blood of Khali and becomes a zombified servant to Mola Ram until Shorty snaps him out of it by burning him with a torch.
I think it is odd that Lucas would change the portrayal of Vader so significantly throughout the series. I know Lucas didn't have a hand in ESB, but he took the character changes there and turned them into something else, and may be back on that ROTJ zombie track with Episode 3. Reading pre-ANH development notes for Star Wars, Vader does go through a lot of changes, but I'm not sure "Zombie" was ever one of them, did Lucas really have this in mind always, or perhaps was there something he saw in Vader in ANH or ESB he thought could be turned into zombification? I don't know, but it seems odd and inconsistant to me.