Surely it's one of those intangibles: although not as much of a youthquake as punk it's kind of similar in that there'll be folks out there who'd argue it was over within a couple of years and anyone saying otherwise is clinging to the rubble of clichés then there'll be others who'll say it evolved into something quite different and then there'll be the diehards dreaming of past glories etc.
In the version of music history that i prefer the Who were right in on the start of psychedelia via the freakbeat feedback solo in "Anyway, Anyhow, Anywhere" (inspired by free jazzer Charlie Parker) – for 1965 they were way ahead of the game and stayed there through the evolution of rock into the early 70s. They didn't come up with the first 'rock opera' though, the magnificent Pretty Things did that with S.F.Sorrow. I'll shut up now before I start going on a bit…