Joni Mitchell, a woman who crossed musical boundaries like a buccaneer, is recovering from an aneurysm. Her 2007 album Shine will probably be her recording swansong. Genius, no matter its age, should be heard.

Shine is the first Mitchell album I heard in full. Like some deeply sonorous whale-call, it's an eerie, charged, improbably exhilarating lamentation on looming, seemingly irreversible environmental failure. Who will come to save the day? The voice is tattered but true. Mighty Mouse? Superman? Swayed by the album's ambience, I decided to listen to her earlier works to see if any came within a big-yellow-taxi-ride.

I realised Mitchell is the Monet of music: for decades, she cranked out masterpieces. Why was that such a surprise? Growing up I'd never heard her records played, let alone raved about. Nobody plumped for her the way they did Pink Floyd or Talking Heads or The Doors. Even in the '90s, when interest in '70s music rekindled, her albums weren't invited to the party. In 2015 nobody gushes about her the way they do Leonard Cohen. Chatting recently with some women in their twenties, I was taken aback to learn none knew of her. Mitchell hasn't exactly been roundly forgotten, but neither is she given due respect. Why?

Let's assume it isn't because she's a woman. And let's say there's more to it than her being synonymous with the flower-child era. Maybe, just maybe, her ungenerous estimations of other respected songwriters have turned a few people off. Some of her not so deferential appraisals are worth a glance.

She referred to Springsteen, at the time he'd made Human Touch, as "a very nice craftsperson." Prince was "your basic hybrid". And of the '80s biggest superstar, "But what's the difference between Madonna and a hard-hooker?" Not hard to guess what she thinks of an artist as physically assertive as Rihanna. But it would be interesting to know how she rates PJ Harvey. How she rates Bob Dylan is plain as day. "Bob Dylan is not authentic at all. Everything about Bob is a deception." Genius sets the bar real high.

How high? Mitchell once said of her work: "I was demanding of myself a deeper and greater honesty, more and more revelation in order to give it back to the people where it goes into their lives and nourishes them and changes their direction and makes light bulbs go off in their head and makes them feel. And it isn't vague, it strikes against the very nerves of their life and in order to do that you have to strike against the very nerves of your own."

But if today's young have overlooked Mitchell's music, it may be nothing more than a reciprocal snub. She's said some less than flattering things about generations since hers. That America's best days may be behind it is one of Shine's motifs. But we have poisoned everything, and oblivious to it all, she rasps, a weary, soothsayer-witch giving the pot a last stir. The cell-phone zombies babble, through the shopping mall. Commercial radio's verdict: no thanks.

Flick around the dial and you won't hear Mitchell. Big Yellow Taxi, her one mainstay, expresses but a fraction of her gifts. More often her lyrics bristle and brim with wit and insight and pathos and passion, and cast the strangest spells. She'll dig to an unpleasant truth. Or disarm with an avowal so intimate it's like a whisper in your ear. She'll pursue and play with metaphor with the flair of a boundlessly gifted poet.

With one well-chosen, weirdly enunciated word she'll manoeuvre a song's rhythm or redirect its mood. A decade before Paul Simon made Graceland she was using African drumming. The uncanny sounds and unbound song-structures on her 1977 masterwork Hejira make Dylan's Blood on the Tracks sound routine. The cover of Hejira has it: a cloaked, august figure with an equine jaw bears the bold expression of one who just seared through self-doubt. A superimposed desert-road journeys inward.

"I cannot even express how your music has touched me," one post reads, on the message board set up since she was hospitalised. Millions share that feeling.