I first encountered Greg's work with Runequest 1st edition in 1979, at a time when I was having serious health issues at University. Playing it helped me cope both psychologically and physically between stints in hospital.
Too young, darnit! The world is a poorer place now he's no longer here, but my goodness, he enriched it so much before then I feel churlish complaining.
My condolences to his family and friends. Other friends, I should say, as though I never met him in person, I did through his magnum opus, Glorantha.
That remains, and I think will rank with the worlds of Tolkein, Swift, Lewis and Barker as an immortal work of imagination.