I don't know who said it, but I'm sure at least one music writer has contended that if he hadn't had those bad acid trips, he could have been bigger than Clapton. Even BB King was a fan, apparently: "[Green] has the sweetest tone I ever heard. He was the only one who gave me the cold sweats."
I feel fortunate that I got to see him play around 1999/2000 - even if he was a shadow of his former self, he still knew his way around the instrument.