Actually, as I said in a post above, I'm happy with this episode. I've read a few things refering to this as a mythological episode, and I think those reviewers are pointing to something they don't quite understand. But that's absolutely right. This episode brings the "myth" of Lost into focus. At least it does for me.
Forget about the mysteries and the plot and all for a bit: What is Lost really all about?
Stories in mythology often aren't entirely logical, they aren't meant to be. They are metaphors, analogies, parables; they are really about the central theme, often human nature. Sometimes they contain aspects of history, sometimes they are pure invention. Some of them seem to fit scientific theory, some of them seem to fit theological belief, some of them are flat out fantasies.
So, this "myth" stages the battle. It isn't good versus evil. It is the natural inherent conflict between duty and free will. Excellent! I'm happy, I get it now.