Directors who basically had one good movie and then never matched that success again?
Michael Cimino - The Deer Hunter
Behn Zeitlin - Beasts of the Southern Wild
Neill Blompkamp - District 9
Richard Kelly - Donnie Darko
Tobe Hooper - The Texas Chain Saw Massacre (Poltergeist is basically not his movie)
Shane Carruth released two unforgettable films then disappeared forever. Perhaps not a one hit wonder but two hit? The Modern Ocean was going to be his big break. Rumors of Keanu Reaves starring. A great loss, a fine example of American cinema in a wasteland of crap.
Cimino is kind of an anomaly. He was a highly competent director but Heaven's Gate devastated his career. Was he killed off by failing to live up to the hype? Something else going on there.
Paul Verhoeven made it to Hollywood with Robocop. Again not another one hit wonder, did a couple good flicks. But got kicked out thanks to Showgirls and Starship Troopers. He was finished after that.