James Mangold’s biopic of singer Johnny Cash has been called this year’s “Ray,” and that turns out to be a pretty fair description of it–or at least of what it tries to be. If you wanted to be flip about it, you might say that while “Ray” was a film about a music icon who was black, “Walk the Line” is one about the icon called the man in black. But to speak more seriously, the basic similarity is that they’re both very conventional Hollywood musical biographies, structured pretty much the same way similar movies would have been back in 1945 or 1959 and presented without a great deal of imagination or any special insight. Both are also notable for the uncannily accurate performances in the lead roles–by Jamie Foxx in “Ray,” of course, and here by both Joaquin Phoenix as Cash and Reese Witherspoon as June Carter (though in neither case would they have been the first names you’d have thought of for those parts). And they’re also likely to be remembered at Oscar time, at least in terms of nominations if not for the statuettes themselves, as Foxx was.

But “Walk the Line” doesn’t match “Ray,” not because it’s any less a slickly professional job but because Cash’s story just isn’t as compelling as Ray Charles’s. With the latter you had not only the man’s emergence from impoverished beginnings but his overcoming blindness, too; and in addition to his inveterate womanizing, his heavy drug usage and his dealings with record companies, there was the racial issue that put the singer-pianist in the context of the most significant element of social change occurring in the country. Cash had troubles in his life, too, but it would be absurd to say that they were in any way the equal of those Charles faced. As depicted here, in a script by Mangold and Gill Dennis based on Cash’s own autobiographical books (which may be the fundamental problem), he must deal with childhood trauma resulting from the death of his beloved older brother (Lucas Till) and the stern, unloving attitude of his alcoholic father (Robert Patrick). And his singing career will not only take a toll on his marriage to his early sweetheart Vivian (Ginnifer Goodwin) but introduce him to the woman who was his true soul-mate and became his real love–singer Carter (Witherspoon), who resisted his advances for years but finally became his second wife. (In fact, the movie seems to be essentially a two-hour difficult courtship.) Cash also had a serious drug problem that threatened his professional and personal well-being. But if you stack up Cash’s troubles against Charles’s, they come off seeming pretty minor. It may even be a shock to learn that despite his famous song from the perspective of a prisoner, Cash never served hard time; he did give a famous concert for the Folsom inmates, but that’s hardly the same thing.

That doesn’t mean that “Walk the Line” isn’t enjoyable, in a modest way. It includes a lot of Cash’s and Carter’s music, which is all to the good, and certainly Phoenix and Witherspoon prove engaging, even remarkable performers, going well beyond mere impersonation. But despite their excellence, the film never goes terribly deep beneath the surface of things; perhaps because it’s based on the singer’s own memoirs, it seems curiously superficial in its depiction of his dreams as well as his troubles. Of course, perhaps what we see here is pretty much all there was. But if so, the Johnny Cash so many people idolize and revere would appear to be more a triumph of showmanship than of reality. Nor is Carter explained any better. She’s resolutely chipper in spite of the fact that she has marital problems; in fact, her biggest crisis seems to arise when the conservative fans of her family puritanically sneer at her for insulting the sanctity of marriage by getting divorced (the movie is especially ham-fisted on this score). Somehow Phoenix and Witherspoon go beyond the blandness of the screenplay to suggest deeper currents in Cash and Carter, but they can’t do it alone.

The supporting cast strikes no particular sparks. Patrick is grim and sour-faced as Cash’s father and Goodwin no better than adequate as the luckless Vivian, while the parade of youngsters who have cameos as other rockers of the era–Tyler Hilton as Elvis Presley, Waylon Malloy Payne as Jerry Lee Lewis, Jonathan Rice as Ray Orbison–seem just like the impersonators they are. Technically the movie is fine, with glossily luxuriant cinematography by Phedon Papamichael and good period production design by David J. Bomba.

But though you’ll probably leave the theatre swinging to the music, this highly conventional movie really doesn’t do its subject justice: it’s a “Ring of Fire” that burns at distressingly low dramatic voltage.