The late 1960s saw a shift in fads from dreamy, extravagant-sounding psychedelic pop full of abstract, disorienting chord combinations to a rock priding itself on being stripped down, honest, and rooted in the tradition of American folk, blues, and gospel. Some bands (Beatles) seemed blindsided by the turn of tastes and did their best to transition gracefully out of their grandiose ways. Some bands (Pink Floyd), paid no attention and opted to redefine psychedelia in the late '60s and into the '70s. Some bands (Hendrix) were grateful to leave the trickery behind and focus more on the roots sounds they were most attracted to anyway.
I think the Doors, differing from all these bands, had the least amount of soul searching to do about this transition. While they did begin adopting a harder blues edge in their later albums, they had always written songs with a certain old-school core (see "Back Door Man" on their first album). While their music did sound psychedelic, it was mostly because they sounded so unorthodox, not because they were cribbing any of the psychedelic playbook. When the time came, the keyboards changed voicing from harpsichord to rock organ; that was really about the end of it.
Look at "Hyacinth House," from the Doors' final album, L.A. Woman.
This is essentially a psychedelic song in the classic Doors sense. It name checks a semi-poisonous Mediterranean plant with a Greek mythological history. The middle organ solo is an extravagant run of classical scales that is more mind-bending than Mississippi Delta. The song's outtro passage is a stirring, unsettling repetition of dark melody far out from where a folk tune would trouble itself to go.
But the plagal chord cadences undergirding the song's verses are so salt of the earth, so unobtrusively pure, that they allow the song to pass in the post-psychedelic world.
Poor Jim Morrison, if there is one song really showing his sense of isolation at this point near the end of his life, it has to be this one. "I need a brand-new friend," is a pathetic, missed cry for help.
But I don't listen to this song to feel down and mopey about things.
This may be one of the most purely beautiful songs the Doors wrote, and I'm obsessed with its sophistication on so many levels. The lyrics are really so well realized, clear, with numerous evocative allusions. The guitar leads are excellent throughout. The organ solo is riveting. The drums pick such a cool down beat in the verses. The soulful vocal is top-notch. And the outtro could play for an hour and I would continue finding harmonies to sing along with.
It all ends with a nice gospel finish, like they'd just been playing us a little church tune.