This is the first volume in the enormous Essential Histories series from Osprey Publishing. If you're considering reading these books, I wouldn't recommend starting with this one. If you do, please realize that this one isn't a very good representative of the series. Most of the volumes are excellent, with a good blend of detailed accounts of individual battles, interesting descriptions of historical figures, and informative information about the general setting and attitudes of the time. This volume utterly fails in all of those categories.
I'm not placing all of the blame on the author however. Osprey Publishing was simply a bit overzealous in thinking that it could cover a series of events that took place over hundreds of years in a single 96-page volume. Whereas the Civil War and Napoleonic Wars are covered in four volumes each, and World War II in six, the entire series of individual crusades is covered in a single volume. What you end up with is a very brief skimming of the overall picture and outcome of the Crusades. Hardly any time at all is spent on individual crusades, much less individual battles (which you get so much of in other Essential Histories).
Also, throughout this book the author downplays the importance of the Crusades to the people of the Mediterranean and Middle East. What he fails to adequately portray is the long-standing and powerful beliefs and feelings that these events have cast on history ever since.
The only really good part of this book is the multitude of excellent pictures, showing everything from architecture to weaponry of the time. Still, of the Essential Histories I've read, this was my least favorite and definitely the least informative. I recommend starting with others.