Joe-Bee One Kenobi points out this article on sfgate.com about George Lucas and Episodes I, II & II:

Part of the problem, Lucas concludes, is that some older "fans" -- a word that doesn't trip lightly from his tongue -- wanted him to start the prequel trilogy with a movie that was substantially less expository than "Phantom Menace." They didn't care to wait another three years for the hard-core mythologizing and breakneck action to kick into gear.

In their impatience, these fans ignored the fact that Lucas had waited nearly 10 times that long for his complete "Star Wars" vision to emerge as one 12-hour story, broken into six more or less equal parts.

The outline he wrote 30 years ago was very specific, Lucas said, so the segment of the story unfolding this week isn't much different from the one originally submitted to Fox executives. Because of budget restraints, Fox merely decided to shoot the end before the beginning.

" 'Episode II' wouldn't have made any sense without 'Phantom Menace,' " Lucas argued. "The prequel is intended to show the descent of a good guy (Anakin Skywalker) into the depths (becoming Darth Vader) in three acts, just like a play. The first act was there to set up all the relevant parts and introduce the characters.

"It's during Act II that the plot thickens, and Act III is when everything comes together. That's going to be the most fun to do."