Short review: I think this is a good corrective book on the crusades. It is well documented but a bit bias toward the crusaders. I think that he has good points and his set up to the crusades (the first 1/3 of the book) was very helpful. He talked about the political situation and the general economic and intellectual status of Europe.
Full review on my blog at http://bookwi.se/gods-battalions-the-case-for-the-crusades-by-rodney-stark/