Revenge of the Sith was great with one glaring exception:
Think about how intimidating Vader was in Episodes IV, V and VI. The main reason for that fear-inspiring persona resulted a great deal from the voice of James Earl Jones. Without that, Vader sounds like nothing more than a squeaky nerd in a helmet.
When James Earl Jones as Vader spoke, anyone watching that movie could feel Vader's presence. You can't have Darth Vader without him. It's be like having Ace Ventura without Jim Carey. Jones' voice defines that character. Episode III - despite bridging the gap between between the first two movies and the trilogy released 20 years ago - lacked the true presence of Vader because of Jones' vocal absense.