Me personally I think artists and albums in late `60 s and early `70s change R`n`R all over the world.I mean the guitar sounds, drum beating , difficulty song composition , rough singing and not in a last place - lirycs.
My favorites : Led Zepp - 1 2 3 & 4
Yardbirds - Almost everything
Black Sabbath - B S - Paranoid - Master of reality
Deep Purple - In rock - Machine head - Fireball
Uriah Heep - Very `eavy very `umble - Salisburry - Look at your self
Pink Floyd - Umma Gumma - Obscured by clouds - Atom heart mother
Nazareth - Rampant - Hair of the dog
and
Sweet - Slade - The band - ELP - Bad Company - Rolling Stones - Yes - Genesis - Rush - Kansas - Boston and many many more.