Matheson’s first three chapters do something I always find very difficult to pull off. He managed to develop a character in isolation, without having any benefit of dialog with another character. The description and narration combine well to bring out poor Robert Neville’s ordinary world.
I think Matheson also does a great job of building up the attackers through their actions (and the one who constantly taunts - “Come out, Neville!”). He makes it through two full chapters before referring to them outright as “vampires”, giving the reader plenty of material to work with before falling into stereotypes of the vampire. By the time we get to the explicit statement, we as readers have been prepared for the idea that these may be vampires, but they’re not Vampires.
There’s one line that really stood out for me, and I’m not exactly sure why:
He took down a can of tomato juice, then left the room that had once belonged to Kathy and now belonged to his stomach.
I think part of it is the language feels a little strange - his stomach has its own room. But it’s also the larger image. The world is in such a state now that what once belonged to an entire human being can now be dedicated to a single organ.