There was a lot of bad progressive rock in the 1970s. It got so bad that punk and new wave arose in reaction, so it was worth it. There was some prog rock that was good amidst all the bombast and dreck. I was a fan of early Genesis, before Peter Gabriel led them into the pretentious Lamb Lies Down On Broadway, then left the group, and Phil Collins took over.
This is Firth of Fifth from Selling England By The Pound.