People often talk about the follow up to this album, Blue, and then Court and Spark as Joni's best works.
This one, her third, is vastly under rated. Her first two albums tend to suffer a bit from underproduction, perhaps intentionally highlighting her coffee house singer/songwriter appeal. But Ladies of the Canyon is a step up from those and a wonderful bridge linking her earlier work to her more popular work.
Without Ladies you wouldn't have Blue or Court and Spark. This album also marks the first time she started to use piano to play and compose on and it really lifts her songwriting talents up a notch: The piano driven For Free, about a popular singer watching a street busker playing for free, is an excellent example. Her voice and piano really shine on this.
This album also includes her classic Big Yellow Taxi and the song made famous by Crosby/Stills/Nash, Woodstock.
It ends with one of my faves, The Circle Game.
This album, to my mind, rates highly with Blue, Court, and Hejira.