John Barleycorn is a tremondous book. One of the first things that will impress you about this book is London's life. London was a literal 'super-man' in the Carlyle sense. This book details how London raised himself from incredible child hood poverty and lower class surroundings while still a teen, engaging in rugged, manly adverntures that were simply amazing. This book also relates how London's love of books changed his life, and it will amaze you that his knowledge is so broad (throughout the book London dazzles us with philosophical qoutes and insights).
Most of all though, this book is about alcoholism. As one reviewer correctly notes, London had a strong liking for intoxication. However, one would be wrong to think of this book as pro-drinking, London is fairly fanatical in his dislike of alcohol and what it eventually did to him and other young men of his age. However, the brilliance of these 'alcoholic memoirs' is that he successfully illuminates the thought processes of most intelligent persons that have drinking problems. You will come away from this book understanding why many people, even an almost super-human person like Jack London, can fall prey to this vice. An absorbing read, and the book has a much more reader friendly and 'modern' style than many of London's fiction.