Lucifer's Hammer

The first half of this book was fairly good - Niven did a good job of setting up characters, and the looming threat of a giant comet strike is handled in a believable, realistic way. After the comet strikes, though, the book kind of devolves into right-wing wank fantasy.

To start off, everyone who's not in the American South either dies off immediately, or is not worth spending any significant time on - the Soviets and Chinese start a nuclear war with each other immediately after the comet strikes; Europe is entirely washed away over the course of a single page; the Israelis and Palestinians find each other to mutual destruction within a paragraph.

Even looking within the parts that do survive, the same sort of devolution is shown - women are treated like property and married off for political considerations, racism is completely socially accepted, and in one bizarre moment Islam is equated with cannibalism.

The only redeemable things about the book by the end are two of the characters: Tim Hamner, the playboy amateur astronomer who becomes a hero, and Harry the Mailman, who refuses to let a little thing like the end of the world keep him from his duty of delivering the mail.