The problem is that Lucas made Anakin shift to the dark side too fast. Remember: according to the original RotJ novel, Padme had grown to fear Anakin so much that she hid her pregnancy from him. In Sith, she experiences fear of Anakin for approximately two conscious minutes.
In the Phantom Menace novelization, little Anakin dreams of Padme leading an army against him. I would have rather seen that play out as the death of Padme than what transpired in Sith.