For many decades Steven Runciman's overview of the Crusades was considered the definitive popular work on the subject, while Runciman himself was the go-to man for Crusades history. However, all that changed in the last forty to thirty years with the rise of better, more thorough scholarly methods (such as computer management of huge amounts of charter information through the use of random-access databases). A new generation of scholars, such as Jonathan Riley-Smith, Christopher Tyerman, Bernard Hamilton, Thomas Madden, Helen Nicholson, Jonathan Philips, etc, have revealed the Crusades to us on a far more in-depth and objective level than was ever attained by Runciman.
Runciman's work has not aged well. His sweeping generalizations and obvious biases have become painfully dated next to the groundbreaking scholarship that has come after him. Runciman was unashamedly petty in allowing his personal likes and dislikes to color his analysis. Within a few pages it's clear that Runciman deeply disliked the Crusaders and favored the Byzantines and Muslims. He attacks figures like Reynald of Chatillon as morally repugnant, meanwhile he lionizes Saladin, saying that his conquest of Jerusalem was "civilized". Runciman fails to sympathize with the thousands of Christian women and children sold into slavery by Saladin at Jerusalem; perhaps they might have disagreed that Saladin was civil. At any rate, it's not for the historian to make morally sharp judgments of character anyway, rather he should attempt to present all sides as objectively as possible, and in this respect Runciman's work is an absolute failure.
What's good about this volume is that it provides a basic, linear outline of the history of the Crusader States from 1100 to 1187. In my writing and research I have used this book as an outline for the period, though I am always deeply suspicious of Runciman's assessments that go beyond mere names and dates. I always check his work against the more current scholarship of professors like Riley-Smith, Tyerman, Philips, and others. I strongly urge all readers of this book to do the same.