Science fiction reaches its zenith when it is commentary by analogy to the present human condition. The original trilogy reached this as it was Lucas' protest of the Vietnam War. This was evident even before Lucas' public statements, from the 1976 novelization and its prologue Journal of the Whills. The prequels were, from the strict standpoint of plot and political commentary, a satisfying fulfillment of this 1976 prologue. That the prequels were released during the Iraq War, a mirror in many ways of the Vietnam War, couldn't have worked out better for communicating Lucas' original 1970's message. Everyone caught on for Episode III, but it was all there in Episode II as well. Episode II was released so soon after 9-11, though, that most people weren't able to key in on it then.
The prequels suffered by having too large a budget. Lucas did better in the original trilogy when budget constraints forced creativity. In the prequels, Lucas felt obligated to have ridiculously short filming schedules for the human actors, and then to leave most of it on the editing room floor so as to not waste all the CGI footage. But the stories in Episodes II & III were outstanding.
Now that Star Wars is in the hands of the Bono-seeking corporatocracy, I have dim hope of any continued criticism of government and monopolies -- and certainly not of any drawing of parallels between the Dark Side and contemporary power structures.