Yes, I was thinking the same thing the other day. A lot of time in "Revenge of the Sith" is actually occupied with last minute attempts to finally show the deep friendship they were supposed to have, which left much too less time for a plausible fall of a hero, because it's just too abrupt and the audience has to buy into the 'forced to turn evil to get the only chance to save padme' thing. I also wonder what kind of revenge there was to see in the film - especially in the light of understanding it as anakin's revenge (in analogy to the jedi's (anakin's) return in RotJ).