This book is simply a classic, and I think that there is little in it that will be overturned by further discoveries about the nature of money. Of course, even if this was to happen, the book will remain one of the best and clearest introductions to the topic of money. The book is also a great example of expository and didactic prose, so it can also be read in that context.
In this book, Rothbard discusses the history and nature of money, and by doing both, explains to the reader what is wrong with the monetary system that the world operates on today. Parts of his writing will be familiar to anyone who has taken a course in economics where money was discussed. However, the more subtle facts about money (the money regression theorem, Gresham's Law, government intereference, the reasons he gives for the government's renunciation of the gold standard etc.) will be new and interesting territory for many readers. Of course, if the ideas of this book are read and combined with the other ideas espoused by Austrian Economics, of which the author was a great proponent, then the truth and coherence of his arguments are very strong.
I strongly recommend this book. Even those (like me) who do not agree with Rothbard's anarchism will find a lot in it that is good.