He will be missed.
As Mark Scott Zecree (sic) noted, Matheson was basically the opposite of Serling on TZ. Serling was the fantasist, but Matheson was the guy who would latch onto a concept and poke, prod, and explore the ramifications of whatever scenario he had set up. Little Girl Lost is probably the example: it's a "hard" science fiction concept that Serling would never have done. Last Flight is another one. But Matheson could also bring the horror: And When the Sky Was Opened is one of the creepiest episodes of the series. And "World of His Own" is one of the funniest TZ episodes, if not the funniest.
And of course, he worked with Shatner twice, on "Nick of Time" (one of the great "is it or isn't it supernatural" episodes), and the classic Nightmare at 20,000 Feet.
Matheson was also one of the four men who created Carl Kolchak, along with Jeff Rice, Dan Curtis, and Darren McGavin. Without Matheson writing the screenplay for the TV movies, Kolchak as we knew him would be a much different person.
Even when writing stuff like Lawman, Matheson was a class act. He did one of the first "real" time episodes of a TV series (Thirty Minutes), and his other stories like Cornered and Samson the Great were also excellent.
And he also adapted Ray Bradbury's Martian Chronicles, which given what he had to work with and what he had to produce for network TV, probably worked out about as well as could be expected.