This was a genre that had so much instrumental activity for so little music that was genuinely pleasurable. The conceit had been that rock had advanced to the degree that it was indeed an art form, concert music, in both the instrumental and lyric sense. This yielded some nice and clever albums and individual tunes that still endure, but in all the mass result was bloat, pretentiousness, ersatz mysticism or bargain bin despair; it was not fun and it was work to listen to. What is amazing is how much work many of us did trying to convince ourselves that most of this material would last beyond our lifetimes. It hasn't. Slate does a nice series detailing the history of the rise and fall and the contents of the progressive rock we all used to love .
I remember the conversations with Steve Esmedina and David Zielinski and George Varga about this stuff; only Esmo defended progressive rock as a genre, on its own terms. I always thought the style was hit or miss for the most part, with the misses, the extended, busy and aimless constructions that occupied the air more than made it sweeter, becoming the norm, rapidly. There were prog rock bands I liked, those being most of King Crimson's career in all their line ups, Yes up to the Fragile album, and smatterings of Jethro Tull, ELP, and so on. What is missing from the story is anything about the American equivalent of British progressive rock; not Kansas or other bands directly copying the Euro style, but rather the likes of Zappa, Captain Beeheart, Steely Dan, Little Feat--the list could go on, of course--but these personalities and bands had the usual devices going for them, like tricky time signatures, off the wall lyrics, impressive instrumental chops, longish and dense arrangements.
The key distinction, though, was the American tradition of blues, jazz and rhythm and blues came to merge very heavily into a mixture that included classical music as a matter of course--what resulted, though, is something altogether different and, I think, a damn sight weirder and less same-sounding than what the Brits were, in time, manufacturing like so many widgets. Let us not forget our glory days of rock/fusion : MILES DAVIS, WEATHER REPORT, TONY WILLIAMS LIFETIME,GARY BURTON, MAHAVISHNU ORCHESTRA, RETURN TO FOREVER; love it or hate it, jazz musicians took up rock dynamics and created a sound that was a fleet, dissonant and complex response to the tinker toy music Europe sent to us. Sure enough, the American version of progressive rock became another version of slick commercialism , resembling the dissonance and explosive virtuosity of the early days and evolving to ever more simple forms, resulting at last in that horrid genre called smooth jazz.