I've been a little antcy about seeing this movie, being a Johnny Cash fan and worrying about how well the impersonations would hold up. No matter how good the soundtrack, script, and cinematography, this movie's effectiveness would depend entirely upon the mimicking abilities of Juaquin Phoenix and Reese Witherspoon. The issue was further complicated by the fact that, unlike, for instance, Jamie Foxx in Ray, Phoenix neither looks like Cash, nor sounds like him, nor is a competent musician.
Of course, David Straithairn did it, acing an impersonation of Edward R. Murrow in Good Night, and Good Luck, but not everyone is David Straithairn.
Despite all that, Phoenix nailed it. Ebert says he couldn't tell it wasn't actually Cash's voice in the soundtrack; I dunno about that, but there was an almost uncanny resemblance there. There is one moment that not only immediately put my worries to rest, but should probably earn Phoenix the Oscar. Before Cash develops his signature sound, he is auditioning in Sun Studios in Memphis, and is asked to play a song he wrote. He clumsily wades into "Folsom Prison Blues," and as the song progresses, he figures out what The Man in Black should sound like, gradually dropping an octave and doubling the pace, and Phoenix transforms into Johnny Cash right in front of our eyes.
As far as the rest of the films goes, the story was good if fairly typical of musician bios, Witherspoon was really good (she was flawless in some really difficult acting moments where she has to walk offstage and onstage, shifting her personality on a dime), and the writers had some fun with the cast (you get to Elvis offer Cash a chili dog during a show and Waylon Jennings letting Cash crash in his hippied-out Memphis shithole apartment).
The best part is, you walk out of the movie with Johnny Cash tunes stuck in your head for the rest of the day.