Retrozap has a new entry in the Power to the Prequels series, “The Prequel Trilogy Worlds of Star Wars”:
The most obvious example of planet-as-metaphor is probably Mustafar, a volcanic setting spewing fire and lava, volatile and unstable. It is an exact mirror of Anakin’s own emotions after he turns to the Dark Side. There is something removed and empty about Anakin as he murders the younglings and masters in the Jedi Temple, but by Mustafar the anguish and revulsion has caught up with him. Note his tears in the aftermath of murdering the Separatists leaders; as he looks out at the churning, heaving chaos of the planet before him, he is provoked to emotion. Wrapped tightly in his cloak, Anakin appears to shiver despite his fiery surroundings.