Philip Roth is a sneaky man. Every time I read one of his stories I spend most of the time thinking "this is the time he really doesn't have anything to say--he's just dragging me along on this obscene journey merely to create a convincing perverted reality." Then I get to the end, and I'm wrong. Again.
Roth has two fixations: sex and Jewishness. These are also the fixations of his protagonist, Alexander Portnoy. While Roth and Portnoy explore sex and Jewishness they lay the foundation for a serious comment on self--or, rather, Self. As amusing as the novel is, its real strength is in constructing such a powerful statement from the petty observations of a self-absorbed narrator.
Funny stuff if you're willing to interpret Portnoy charitably. If not, this will just aggravate you.