For me, this is unexpected and terribly sad news.
Upon just reading of his passing, I thought to myself how I would characterize his artwork to a layperson. Consider three vastly different artists who I adore mostly because of their work in the silver age. Curt Swan drew in more of a caricature-styled realism perfectly suited for the younger audience of early DC silver age readers. Jack Kirby breached the fantastical, creating new universes, with his heroes seemingly jumping off the page. Everything was imbued with power and a heightened sense of drama. Neal Adams’ artwork was every bit as game-changing, but in a drastically different manner. I can best describe his style as a sort of “kinetic realism,” for want of a better term. Neal didn’t draw static images: everything was drawn as if it was in motion, just like the stories he illustrated. His facial expressions were rendered beyond compare (Andrew Loomis level actually), and his anatomical prowess was every bit as skillful. He was gifted with a repository of incredible natural talent, and, as others have stated, left us with one of the most enduring legacies in comicdom.
He will be both missed and forever revered.