Johnny Cash was the man, “steady like a train and sharp as a razor”, with his guitar he waved around like a rifle, his deep voice and that steel-eyed stare. He’s a country music legend and he acquired further cred in his later years as kind of a damned poet, singing of death and desolation with chilling conviction. What’s maybe not as well known is that he got his start as a pop star, touring with fellow founding fathers of rock & roll Elvis Presley, Jerry Lee Lewis, Roy Orbison and Carl Perkins. This is one of the most interesting things in “Walk the Line”, an otherwise not that illuminating biopic.

You see, back in the 1950s, there were no fancy tours with roadies and buses and high-tech gear. You just had these young men crammed in a car, driving around the country and playing to hysteric crowds of screaming girls. This is what we see in the middle part of the movie and it’s as fun as it sounds, especially with all the great songs. Director James Mangold screwed up a few things with this movie, but one decision he made that was absolutely right was to have all the actors sing their parts, live on the spot most of the time. This gives the musical scenes a lot of energy, with actual sweat and tears going into the performances before our eyes.

To pull this off, of course, Mangold needed to cast someone who could measure up vocally to Cash, and he found him in Joaquin Phoenix. We knew the guy had acting chops, but who knew he had such a great voice? Phoenix is riveting, capturing the mystique and raw power that made Cash such a unique presence and doing justice to all of his great tunes. Equally amazing is Reese Witherspoon as June Carter, the angelic child star who grew up to become Cash’s sassy bandmate and, eventually, his wife. Witherspoon shows off all her skills in this role, comedic, dramatic and yes, musical. The girl oughta record an album, I’d buy it in a minute!

Understandably yet somewhat unfortunately, Phoenix and Witherspoon can’t spend the whole picture on stage. Before Cash gets involved with the Sun Records gang in Memphis, we see him as a child working with his hard-ass father (Robert Patrick) in the fields and singing hymns with his mother (Shelby Lynn), going fishing with his beloved brother, whom he loses in a tragic accident. Later on, Cash does his military service in Germany and marries for the first time, to a nagging shrew (Ginnifer Goodwin) who does nothing but bust his ass about everything. No wonder he longs for the adorable June, who doesn’t take shit from everyone but is at least able to have a good time.

There is a lot of episodic stuff about Cash and Carter growing closer then being driven apart over the years, as her shame of being divorced and his addiction to amphetamines, among other things, stop them from taking the intimacy they share in front of live audiences off the stage. Most of these scenes are okay, thanks in no small amount to Witherspoon and Phoenix’ chemistry, but there are some real groaners in there. “You can’t walk no line!” Ugh. And as much as they show Cash tearing up bathrooms, breaking beer bottles, kicking microphone stands and smashing foot lights, driving a tractor into a lake (don’t ask), etc., we never truly feel his demons on more than a superficial level. This movie’s idea of depth is having the protagonist sit in his yard, lost in thought, with stock sounds of squawking hawks in the distance.

Still, all that generic biopic stuff and even the awful “ending” can’t take away from the joy of watching Joaquin Phoenix and Reese Witherspoon singing together. These musical scenes alone make “Walk the Line” well worth seeing.