I certainly read him; his SF novels of the 1960s and 70s, particularly Camp Concentration and 334, had an enormous impact on me. But “least read” may be true: according to publishing legend, his SF masterpiece On Wings of Song had a 90% return rate in its 1980 Bantam paperback edition. Despite that, he went on to hit bestseller lists with his 1991 horror novel The M.D. Just as unexpectedly, his children’s book The Brave Little Toaster was adapted into a popular Disney cartoon.Link
He could be hard to take, both in person and in his public interactions with the SF world. He played the game of literary politics hard, and sometimes lost badly. He frequently seemed to have no patience for his allies, much less his enemies. Of his other career, as noted poet Tom Disch, I can’t say much, except that to my mind the poetry was often good. In his later years he wrote a blog; after he began to post frequently on the depravity of Muslims and immigrants, I became unable to keep reading it.
The Disch I prefer to remember was no nicer than that, but much smarter: a brittle and brilliant ironist with a bright wit and no optimism whatsoever.