CO said:

In many ways, the Saga started at Episode II because that is when you get to the nitty gritty of the main characters, and that is the biggest flaw of the Prequels.

I agree. However, I can also see what Lucas was aiming at; he wanted to show someone who turned out "evil", who started out as a normal kid - but by degrees, he slowly got corrupted through choices that he thought were right at the time. It didn't really work, of course, for various reasons, but the goal makes sense.