Genesis - "Selling England By The Pound"
This was before Peter Gabriel left and the rest of them decided to change the band's format from concept rock to...
...let's see, what was it?
Oh yeah. Crap.
The Lamb Lies Down on Broadway!!!!!! - Way ahead of it's time. Genesis declined not so much when Gabriel left, Trick and Wind and Wuthering were among some of their best work, but once Steve Hackett left, that's when it went downhill.