This documentary focuses on British progressive rock of the "classical" age of progressive rock, which is only fitting, because progressive rock was born in England, made world famous by British bands, and (apologies to all the rest) the cream of progressive rock, at least in its heyday, was created by British bands. Yes, there are prog bands making good music today, and they're not all (or even mostly) British, but I'm sorry to say, they will never reach the peak of the classic era, either in fame or in creativity. The bands of classic era made the blueprint, and all others follow it, no matter how much they tweak it or try to get away from that basic blueprint. I have wondered if the bands today (and not just progressive bands, but most all rock bands) don't live, eat, breathe their instruments the way the musicians from the classic rock era did. Many of the British musicians (who were usually the virtuosos) grew up in Britain under rationing, so what was there to do but become obsessed with your instrument? And progressive rock, like no other genres except perhaps bluegrass and classical music, requires mastery of your instrument. Good progressive rock won't happen if the band's instrumentalists (at least most of them) can't play well. A foundation in classical music doesn't hurt either. Add to that, you must have a rock sensibility. A fantastic drummer like Bill Bruford can easily work in the jazz world with its tricky time signatures, and then bring them to progressive rock.
Anyway, this great documentary touches on some of that, and has some informative and often humorous interviews with the members of the prog world, from its heyday. And I personally always thought that Rick Wakeman's capes were rather endearing.
