I've also only read I Am Legend (quite recently too). Here's what Stephen King had to say about it:
Originally posted by Stephen KingWe've lost one of the giants of the fantasy and horror genres. From THE BEARDLESS WARRIORS, his brilliant (and largely unread) World War II novel, to THE INCREDIBLE SHRINKING MAN and all the wonderful TWILIGHT ZONE scripts and stories, Matheson fired the imaginations of three generations of writers. Without his I AM LEGEND, there would have been no NIGHT OF THE LIVING DEAD; without NIGHT OF THE LIVING DEAD, there would have been no WALKING DEAD, 28 DAYS LATER, or WORLD WAR Z. Matheson wrote the script for Steven Spielberg's extraordinary film, DUEL, and created one of the most brain-freezingly frightening haunted house novels of the 20th century in HELL HOUSE. He fired my imagination by placing his horrors not in European castles and Lovecraftian universes, but in American scenes I knew and could relate to. "I want to do that," I thought. "I must do that." Matheson showed the way. In addition to that, he was a gentleman who was always willing to give a young writer a hand up. I will miss his kindness and erudition. He lived a full life, raised a fine family, and gave us unforgettable stories, novels, TV shows, and movies. That's good. Nevertheless, I mourn his loss. A uniquely American voice has been silenced.
Yeah, he had been sick for some time. I read that Wizard article a year or two back after his relapse, and it was a hard read...he was talking about going to cons, but being too weak to stand. I was pulling for him. Shame that he's gone.