5. John Singleton (Boyz n the Hood)
At the mere age of 24, John Singleton became a dual Oscar nominee as writer and director on the superb crime drama Boyz n the Hood, yet since, pretty much every single film he's made has become more generic and broad than the one before it. If his first three follow-ups - Poetic Justice, Higher Learning and Rosewood - were watchable "race movies", then the Samuel L. Jackson-starring Shaft is where it all started to go wrong. Passable but broad, Singleton then eventually embraced his career trajectory and directed 2 Fast 2 Furious, one of the worst entries in the entire series, before helming the forgettable Mark Wahlberg-starring crime thriller Four Brothers, and finally, committing cinematic hara-kiri with Abduction, a feckless Taylor Lautner vehicle that is so anonymously directed you'd never guess Singleton was at the helm (which is probably a good thing for his sake).