The "fatal flaw" for me was the bullshit Lucas was spewing about how the films should rhyme. Namely the fact that Luke and Anakin both grew up on the same planet. Just like poetry.
The very fact that Darth Vader (AKA Little Orphan Ani) does not wonder about the significance of the Tantive IV coming to Tatooine. Or that even with his high midi-chlorian count (higher than our little green friend), he can't sense that his former mentor, son or brother in law (and his girlfriend, Beru) live on the planet that he was miraculously conceived? Bull-to-the-shit!
And let's not forget that he can't sense that Leia is his daughter when she is within strangling distance.