Further to His Excellency Simon's post below, here's the aural equivalent of drinking a litre of Sunny Delight, and doing somersaults on a bouncy castle:
"Ma Kelly's Greasy Spoon" (1970) is the most intriguing Quo album, as it indicates some of the directions they could have taken as they felt their way out of their strung-out psychedelic phase. This song is surprisingly minimal/brutal, and not at all good-timey:
"Dog Of Two Head" (1971) was the first album where they began to find their way. There then began the band/fan alchemical process of mutual appreciation, refining their riffing until they extracted the molten gold of "Down Down".
The Quo hung around too long of course, and even worse, still made hits as they did so, an unforgiveable crime in those far off days when pop temporality and the idea of musical "progress" actually meant something. In the '90's they were put on an unofficial Radio 1 blacklist (along with Sir Cliff), because new controller Matthew Bannister wanted to make room for bold, innovative new groups like The Bluetones and Shed Seven.
Still, for dirty-kneed 70's schoolboys, there was only one band that rocked our world: