Biopics are bad enough, but biopics about genius artists tend to be the worst, and biopics of genius artists who are particular icons to the Baby Boomer generation? You might as well try to survive a nuclear strike. So the simple fact that Love & Mercy, the story of Beach Boys songwriter, producer, and artistic guide Brian Wilson, is pretty damn good - not great, but pretty damn good - is beyond miraculous. And I haven't even mentioned yet that it drags two remarkable-unto-sublime performances out of Paul Dano and John Cusack, a pair of actors whose recent career choices would leave me unwilling to trust them with doing voiceover work for a McDonald's ad, let alone bringing to life one of the defining artists of 20th Century pop music.

Aye, they both play Brian; that's sort of the gimmick, you see. Love & Mercy splits itself into two parts that interweave, each covering a short, important window in Wilson's life. There's the period in the 1960s (the Dano half) during which he conceived and created Pet Sounds, the "Good Vibrations" single, and the increasingly deranged recording sessions for the unrealised Smile, at which time he transformed from "guy who has auditory hallucinations that he funnels into his daringly unconventional production of rock & pop music" into "guy who has auditory hallucinations that leave him unable to function at the most basic human level". And then, there is the period in the 1980s (the Cusack half), which finds him overmedicated and easily manipulated by the overreaching Dr. Eugene Landy (Paul Giamatti), and befriended by Cadillac salesperson Melinda Ledbettr (Elizabeth Banks), who figures out reasonably quickly that he's being horribly mistreated, but has no idea what to do to help him.

The most critical thing that Love & Mercy gets right, and it's apparently all on director Bill Pohlad (who is, by habit, a producer) that it got that way, is that it's not a story of how Brian Wilson was a genius who used his emotional torments to feed his genius and thus created the genius works that have made all our lives better for a half-century. Now, I happen to believe that Pet Sounds is one of the handful of perfect musical objects of the last 70 years, and that "Good Vibrations" puts in an enormously strong case for being the finest pop single ever recorded. And because I believe that, there are some in-jokes and one-off references in Love & Mercy that I get to enjoy more than other people. But in virtually every way that it effects the story or the treatment of the characters, the film doesn't reward me for having good taste. It matters, within the film's frame of reference, that Pet Sounds is generally regarded as a masterpiece with songs on it that a random person, e.g. a Cadillac salesperson, would immediately recognise, and have automatic enthusiasm for meeting the man who wrote them. It does not, however, matter what we think.

Given the crushing volume of biopics, and musical biopics especially, whose solitary hook is "because this person achieved great things and you love him/her for it, come bask in hero worship for two hours", the existence of a movie that takes an unbelievably famous man and prefers to place him in a character study that feels the need to make the case in reference to itself that he deserves to be studied is great enough. But then Love & Mercy goes even farther in the direction of the angels by focusing, rigidly, on just one aspect of its subject's personality and building its narrative around relatively concise stretches of his life that directly relate to that one aspect. This merciless focus serves the movie well as cinema, far better indeed than the macroscopic "childhood to the grave look of virtually every other biopic of recent vintage. Praise be to Pohlad for having the good sense to make those choices, and praise be to screenwriter Oren Moverman (who also co-wrote one of the only other mainstream biopics of the 21st Century that's worth keeping, the experimental Bob Dylan fantasia I'm Not There) for executing it so successfully. Even without recourse to its terrific cast and its occasional unconventional technique, the structure and narrowed scope would be enough by themselves to put in a play for this as the most original and insightful film biography in many, many years.

In the form of Dano and Cusack, it boasts two absolutely vital performances that are not any kind of mimicry - Cusack does not physically resemble Wilson at any stage of his life - and aren't interested in digging into the creative process. They are performing a man with a profound mental imbalance, in both cases putting more emphasis on his personhood than his disease. And, forbidden by Pohlad from meeting to build the character together, the actors approach that goal with sufficiently different strategies that the break in personality is shocking and even scary, hammering home the idea that the years between Smile and Lebdetter's arrival represented a profound, irrecoverable rupture in Wilson's life more eloquently than any piece of writing could. It's career-redefining work for both men; Cusack hasn't played so hard against his stock tricks and refrained from indulging in his standard persona in years and years, and it's the most daunting, accomplished performance that Dano has ever given in a movie.

And even given that, I'm not sure if I'd hand either of those men Best in Show honors over Banks, who emerges as the actual protagonist of the 1980s scenes, in a role that demands different things of her than I can recall having ever seen. There's little to no comedy in the movie, which hamstrings her from using her best-honed tools; but the quick-witted reaction times and disappearance into the needs of the individual moment that mark good improvisation translates remarkably well to the needs of a sober character drama.

Stylistically, Love & Mercy is a bit subtler; Pohlad and cinematographer Robert D. Yeoman aren't hellbent on putting together particularly striking images, and while the movie is unmistakably well-shot, it's in a very humble manner that only goes for broke in a couple sequences that try to mimic '60s film stock. Otherwise, it's all so many California afternoons with thinnish yellow and blue skies, well-used but hardly imaginative. Where Love & Mercy casually sidles into genius is in its sound design, led by Eugene Gearty, as befits a movie about a man driven towards crafting innovative overlays and harmonies in pop songs because it captured the world as he knew it, with its shifting, non-real sounds. The movie calls attention to audio first and foremost: it's opening is a black screen on top of which a formless sound montage rolls around over our heads and behind our ears and back and forth through our skulls. And this continues, if frequently in less aggressive forms, throughout the movie, sometimes for better (young Brian's fit in a swimming in a pool), sometimes not quite as much (a busy, noisy dinner that feels a little bit too "yes, we get the point, thank you"). It shades invisibly into Atticus Ross's astounding, perfect score, a sound collage using fragments of Beach Boys hits and incomplete session tracks that have been reassembled and tweaked so much as to sound like the movie having an auditory hallucination of its very own, one from which snatches of music can be pulled out only if we're paying attention constantly. It's a marriage of form and content of an unexpected sort, but it works perfectly to match our perception to the distressed leads'.

The question that at last presents itself: does all this add up to an actually great piece of cinema? Or am I simply bowled over by a semi-biopic that breaks every last one of the conventions that makes that my least favorite genre, and find myself anxious to overrate it? For all that I'm thoroughly impressed by Love & Mercy and have had it rolling around in my head much more stickily than I'd have ever assumed might happen, I can't quite bring myself to actually recommend it. Still, it's better than it has any right to be in virtually every capacity, and far be it from me to undersell that kind of achievement.