Except for his books about writing, Gardner is mostly out of print now, though a recent memoir by his last wife (reviewed at Amazon by his first wife) and a new biography have tried to bring more attention to him. Gardner would probably find it sad that his books on writing have been tremendously influential (just in the SF world, Mary Rickert mentioned The Art of Fiction to me, and at the recent World Science Fiction Convention David Marusek brandished a copy during a panel and recommended everyone read it) while his fiction has been, for the most part, little more than a footnote to the literary history of the 1970s and early '80s (Grendel has been popular in classes that study Beowulf).
One of the best short story writers in the U.S. right now, Jeffrey Ford, studied with Gardner and was first published by him in Gardner's magazine MSS.. Readers of this site are probably more familiar with Jeff's novels and his magnificent short story collection The Fantasy Writer's Assistant than with Gardner's fiction, but here is what he told Jeff VanderMeer in an interview a few years ago about his former teacher:
Gardner trashed just about everyone who was anyone, including himself, at some point. If Pablo Picasso never got called an asshole, it wasn't Gardner's fault. Gardner brought a bad rap on himself with all that Moral Fiction crapola. I never paid much attention to it and it never really came up in any discussions we had. I think he liked to stir the shit sometimes for fun, sometimes for notoriety, sometimes out of a sense of perverseness. He was, at once, a very good person and a very troubled person. His mind was spinning 24/7. If you go back and look at the writing of that period in the seventies, he was probably one of the most innovative of fiction writers. He was also writing essays, poetry, opera librettos, plays, radio dramas, you name it. I was never much for some of his more lauded works like The Sunlight Dialogues , a real brick of a novel, but I really love The King's Indian, Freddy's Book, Mickelsson's Ghosts . The last mentioned is one of the wildest fucking books in American Literature. I found its structure and story mind altering. Its style is deceptively at home, but it is really a wolf in sheep's clothing.
Above all else, Gardner was a great teacher of writing (not just my estimation but also attested to by scores of his students, including Raymond Carver). I'd take him these thirty page stories written in pencil on torn out sheets of notebook paper and slip them under his office door. Then, who knew when, sometimes late at night, once in the middle of a blizzard, he'd call me and say, "I'm reading your story." I lived in a motel across the highway from the college and I'd just drop what I was doing and go. Then he'd sit there with a pen in his hand and go through the lines of the piece one by one. He was brutal, but not without a sense of humor. By the time he'd be done, there would be about five lines left. "These are good," he'd tell me. "Write another one." Eventually he told me he wouldn't read them anymore unless I typed them up. It's got to be rare to find a writer of his caliber who would spend the amount of time he did with students. He'd spend hours going over a single story with you. So many of the things he told me about writing I didn't understand at the time but they come back to me now and I just shake my head at how true they were. He'd say weird stuff too, like "I believe that consciousness exists outside the body and it plays the physical being like an instrument." It made me wonder if everything he told me was total lunacy, but, luckily, I was dumber than a sac of shit and knew it, which allowed me to just push forward and trust him.