I Am Legend seems to be mostly concerned with the human response to isolation, and I found Matheson's take to be a little disturbing. Neville is understandably dealing with crushing grief, fear, and loneliness, but his response to the female vampires was...excessively rapey. It was off-putting and hard to relate to; this might say something about the time in which the author lived (IAL was published almost sixty years ago), or maybe Matheson just has issues, I don't know. Anyway, Neville eventually finds a measure of peace in the search for knowledge, teaching himself science in an attempt to understand the how and why of his world's transformation.
The story ends abruptly: Neville is discovered and killed by a community of "civilized" vampires, who fear him and his hunting skills. It felt to me like a missed opportunity to explore xenophobia and the human instinct to destroy rather than communicate.