The prequels don't fail purely on a visual level, they fail at telling a good story, having good acting and a good screenplay.
The only film in the whole bunch that seemed to have any humanity at all was the phantom menace and was the only one that was a film, but still was a big drop in quality from return of the jedi.
Hayden Christensens's acting i find to be so painfully bad i cannot even watch episode II or III without wanting to hit the mute button whenever he talks.