I'm about half-way through Matheson's 1954 pulp, I am Legend and must say it's very readable racy stuff. It's also rather different than the two film versions I've seen (Omega Man and I am Legend).
Two things are immediately noticeable regarding the plot and the way it's organised: in the novel the character spends a lot of time researching garlic, crosses, etc--the usual vampire props. That might have been interesting in the 1950s but isn't these days: the bio/virus/lab parts of the recent (2007) film are a positive and much more convincing improvement; on the other hand, the protagonist, Robert Neville, is much more of a man in the novel. His wife and daughter are dead, and the creatures who see him as their prey regularly try to tempt him sexually, knowing that he's vulnerable in this regard. In fact, the novel has an eroticism that shimmers below its surface and accounts for much of the characters' tensions. In both films this element is played down almost to the point of extinguishing it altogether. OK, so both Charlton Heston and Will Smith notice shop mannequins but not much is made of it. In the novel, Neville is aching for female company. This human element, this identification with the main character, is one of the reasons why this particular novel has survived. The story is also well-paced and structured, so that reading becomes compulsive-- another plus.