I've read several. Was a student of his when A Childhood; The Diary of a Place was published, started and finished it the day it hit the book store. That's the best place to start. It's a masterpiece, was the New York Times Book Review's non-fiction book of the year. I've read A Feast of Snakes, Car, The Knockout Artist, Scar Lover, The Mulching of America, Celebration and a few others whose titles I can't recall. I've also read a few anthologies of essays and magazine articles he wrote for Esquire and Playboy. Still own two of those anthologies, Florida Frenzy and Blood and Grits. My favorite piece was his contribution to Esquire's series "Why I live where I live" which naturally was about Gainesville. The first sentence is would make William Faulkner blush, lasting nearly an entire page.
It's heady stuff, definitely not for everyone, but he was a giant among late 20th century authors. He's universally considered the best of the Post-Agragrian southern writers and was actually mentored by one of the original Agrarians, Andrew Lytle.
Still holding out hope another one of his books will be adapted for film. The Hawk is Dying was adapted, very poorly and with a very small budget, with Paul Giamatti directing and playing the lead. Harry had some big fans and backers at American Zootrope, mostly notably Sean Penn who was very close to Harry. Sean got The Knockout Artist into development, but it never went to pre-production. Harry actually made a lot of money writing screenplays that never got produced, mainly because of his relationship with Penn.
Sean has a lot more influence now and is regarded as a fine director. If he wants it done, Coppola will probably fork over the money. They'll just have to pick the most film-able and marketable material. I think the Knockout Artist would be a good film, as would Celebration.
Films or no films, Harry will eventually be more famous as a dead author than a living one.