Episode III did not fail the star wars saga, George Lucas did.
He was seduced by the darkside of cgi and crappy storylines, sold the new films to the lowest common demoninator to make the highest profit.
When star wars was made in 1976-77 they were not even sure it would break even. Lucas had feared the production would get shut down and the movie would be taken away from him and reedited as had been done on thx 1138 and american graffiti. That movie was made with an adventurous spirit and a heck of a good story, the prequels are farts in the wind compared to star wars and empire strikes back.