Casting hurt, a lot. A more credible Anakin (at both ages) would have helped immensely. If you simply can't believe that Anakin is incredibly talented and capable - that it's possible for him to grow up to be Vader - the movies can't work, even if you have great scripts (and they didn't). It's like casting Pauly Shore as T.E. Lawrence and expecting Lawrence of Arabia to be a good film.