Joseph Bottum remembers, over at First Things.
Simply as a piece of argumentative prose, the 1968 encyclical was badly constructed. It lacked the romantic elements that Pope John Paul II would later put in his far more persuasive Theology of the Body, and it appealed to the authority of Christian tradition at a moment in which hardly anyone was willing to listen to authority. Still, along the way, Paul VI issued four general prophecies in Humanae Vitae, and on about all four of them, he seems to have been right.