Where would Timberlake as Elton John rank in misguided music biopic casting? (Photo by Ronny Hartmann/Getty Images)

We're rooting for Robert Downey, Jr., but Justin-as-Elton isn't the worst casting idea we've ever heard, or the most potentially awesome. It does make plain the difficulties inherent in casting musical biopics: Timberlake is a singer and dancer of great talents but an actor of limited range, and if the greatest recent biopic performances (Marion Cotillard as Edith Piaf, Gary Oldman as Sid Vicious, even Jennifer Lopez as Selena) have taught us anything, it's that the latter skillset is more important.

With that in mind, we've taken a look at five of history's worst, awkwardest and most downright unwatchable music-related biopic casting choices. Things we left out: Anyone who played Bob Dylan in "I'm Not There" (maybe everyone was great? We couldn't get through it):

Dennis Quaid as Jerry Lee Lewis, "Great of Balls of Fire"

We're actually on the fence about this one. Quaid was hammy and unlikable, but so is the Killer. And the film itself was entertaining. In retrospect, though, just too broad.  

Russell Crowe as himself in "Texas: Thirty Odd Foot of Grunts"

Crowe is just generally unbearable. This 2001 documentary, chronicling the exploits of his now-defunct band, only made things worse.

Hayden Christensen as Billy Quinn in "Factory Girl"

Christensen played a fictionalized version of Bob Dylan in this Edie Sedgwick biopic. Dylan's lawyers threatened to sue, though Christensen's wooden performance probably wasn't why.

David Bowie as Andy Warhol in "Basquiat"

Not his fault — has anyone ever done Warhol justice?

Val Kilmer as Jim Morrison in "The Doors

Bloated and unpleasant and awful. Worse in retrospect, and that's saying something.