The fatal flaw is that Star Wars became a vehicle to making toys, so instead of having toys based off film characters. The films were made with the concern of, what looks good and sells toys.
The biggest problem with TPM is the Pod Race, essentially Lucas wanted a Pod Race, and so tryed to come up with a contrived Plot which would let him have a Pod Race in there. That's why there is so much pointless dialogue on Tatooine as he trys to contrive the reason for the Pod Race.
AotC sucks, because frankly Star Wars is called Star WARS - yet two thirds of the film goes by before there is a WAR... Instead we have to put up with a lack lustre love story with horrific dialog and crap acting. Of course I do feel sorry for the actors in AotC and RotS, cant be easy to act when all you have is a stick and a blue screen.
RotS just left itself too much to do, and we didn't see enough of Vader hunting down Jedi... IMO most of that film should of been after Vader had turned and him hunting down and killing Jedi...
This then moves us into the fact Star Wars being made exclusively as a kids film - with all the horrible crap that started in RotJ... What amazes me, is Lucas doesn't seem to realise that kids loved ANH and ESB - He didn't have to talk down to them, or have crap humour, or teddy-bears beating an "entire legion of my best troops" for them to love Star Wars. Then suddenly Lucas seems to of realised in RotS he needed to go "adult again" to finish it...