Here to second the all the preceeding comments. Saw Joni at the Felt Forum a few years back when she was on the road for Both Sides Now--amazing how she can combine the wit and creativity of the true artist with the gravitas and presence of almost an eminence grise of the music world.
Her smoke-ravaged voice, as Orion and JoeKv have noted, brings an incredibly moving and powerful note of world-weariness and painful experience to lyrics that were written full of hope and optimism. She couldn't have been planning it that way, but it simply a brilliant artistic touch.
So much of her fame as a song writer, of course, comes from the interpretations of her words by Others, and the TNT "Salute to Joni Mitchell" contained a number of revelatory performances, in particular a shattering "Case of You" by Diana Krall--born to sing that song--and a show-stopping "Carrie" by Cyndi Lauper. Both are available at iTunes, I believe, and I encourage the Joni Lover to purchase these two recordings, turn off the phone, pour a glass of wine and lose yourself for a while.
Finally, while getting a mani and pedi at "Nails" on W. 55th street/7th Ave. last year, who should sit down in the pedi chair opposite, but Ms. Joni Mitchell. Literally shaking with excitement, I put myself forward and showed her that my iPod was paused at the song I had been listening to on the way uptown was "Free Man in Paris". Precisely the smart, scratchy, personality you would expect her to be, she was very excited by the whole iPod thing and chatted with me like an old friend. Another reason to keep your cuticles trim.
"They have never understood, and no reason that they should.
But if anybody could . . . " --SS