I came to Matheson through the old 'Twilight Zone' reruns and was blown away when I tracked down his original stories. For pure horror fans, the non-negotiable start is 'I Am Legend'. It's not just about vampires; it's this crushing, clinical study of loneliness and the psychological erosion of being the last "normal" man. The ending redefines the entire book in a way most adaptations totally whiff on.
After that, you have to hit 'Hell House'. It's a masterclass in escalating dread, taking the classic haunted house setup and injecting it with pseudo-scientific ghost hunting. The characters are all deeply flawed, which makes the house's assaults feel personal and deserved. It's grimy, mean, and has one of the most unsettling antagonists in any horror novel I've read.
'What Dreams May Come' is a different beast—more spiritual horror and a deeply weird afterlife travelogue—but its sheer imaginative weight is haunting in its own right. For short stories, 'Nightmare at 20,000 Feet' is iconic, but 'Duel', the novella, is this perfect, bare-knuckle exercise in paranoia. A lot of his stuff feels like it's happening in a sun-blasted, rational world that's just started to crack at the seams, which somehow makes the horror hit harder.