American Idol (I never watch, just heard about this on the intertubes) did a Neil Diamond thing.
He turned into a parody of himself by the mid '70s, yet wrote some great music. And was recently rehabilitated by Rick Rubin, into relevance again.
So here's some vintage Neil:
Compare/contrast, please, with these guys doing the same song:
And for real geeks, here's another version by Deep Purple. Nice recording, but Blackmore's guitar solo is fairly weak.