France's work is certainly the best military history of the 1st Crusade in print. Contrary to popular belief, many nobles of the First Crusade did indeed have experience leading and/or fighting in organized, well led military ventures in Europe. Robert of Normandy and Robert of Flanders were both experienced campaigners. Duke Godfrey of Boullion was at the great Siege of Rome, and Bohemond of Taranto (clearly the Crusade's most able tactician) had long experience fighting against his Guiscard relatives and the Byzantines in the Balkans. France admirably refutes any idea that the 1st Crusade was simply a horde of fanatical barbarians. He does a fine job of explaining how relatively large-scale logistics and planning were skills that a number of nobles brought with them to the East. In fact, the ultimate success of the venture could not have happened without such expertise. Understanding this fact helps the student realize that the 1st Crusade's success cannot be entirely attributed to (a) religious fanaticism, (b) Islamic divisions, or (c) luck (all of which many past historians have subscribed). Certainly, all 3 of the above were factors, but none of them can fully explain the amazing success of the late 11th century European knights in Turkey, Syia, and Palestine. As France explains, martial skills conquered the Holy Land. Other considerations, from a military perspective, are peripheral. The religious fanaticism of the crusaders certainly helped them in their conquests (defeat of Kerbogha, especially), but such fanaticism couldn't defeat an enemy alone. After all, the People's Crusade (1096) of Peter the Hermit had equal fanaticism, and it was cut to pieces almost as soon as it stepped on Turkish soil. By the same token, Islamic political divisions after the death of Malik Shah certainly contributed to the Crusade's success. However, even with such divisions, the Crusaders were at huge numerical and/or resource disadvantages against their Islamic opponents. After all, the Crusaders were often outnumbered, were fighting thousands of miles from home on unfamiliar terrain, and had virtually no supply line. It took leadership and force of arms for such wondrous military achievements to take place.
France does about as good a job of analyzing the military decisions and actions of the Crusaders as I have read. He covers in detail all of the major clashes (along with many minor ones) with Islamic powers: Nicea, Dorylaem, Antioch, Jerusalem, and Ascalon. Battle tactics and strategy are well covered, maps are understandable and relevant, and results are clearly explained. France, like other historians, recognizes that the European's greatest asset was the heavily mailed charge. The Crusaders were rather more heavily armoured than their Islamic adversaries, and the charge was a devastating weapon. However, the heavily armoured charge was in somewhat of an embryonic stage in the late 11th century and certainly wasn't yet what it would be come in the 12th and 13th centuries. Because it was a relatively new innovation, it took quite exquisite leadership and martial ability to use it effectively. It took even better generalship to coordinate the cavalry with the infantry. One of the greatest strengths of France's work is his coverage of how these skilled soldiers (Bohemond in particular) were able to link cavalry actions with infantry actions and how the Crusaders quickly and continually learned these lessons after encountering the Turks' alien fighting style. The lightly armed Turks presented the Crusaders with an opponent that they had not seen before. They were highly mobile and fought primarily from the saddle with a composite bow. Their tactics frequently involved encirclement and feigned retreat. These were tactics, in fact, that troubled European knights for 200 years in the Holy Land. Still, the 1st Crusaders were able to modify their own tactics enough to clear the way of Turks on their way to Jerusalem. Again, such adaptation shows just how militarily sophisticated and skilled these Western "barbarians" really were. Again, a strength of France's work.
On the negative side, there was not enough comparative study of the weapons available to Christian and Islamic armies. We are told that the Europeans were rather more heavily armoured than their Islamic opponents and that they typically carried far heavier lances. However, there is no detailed discussion of these issues. Short mention is made of mail and lamellar, and very little comment is made about relative hand weapon size/construction/type/etc. That said, France certainly does not believe that military technology was a decisive factor in the Crusade's success. Hence, he can't be faulted too much for not including information not relevant to his thesis especially when he considers technological differences to be either non-decisive or negligible. France also tends to get ahead of himself in parts of the work which may cause some to question its focus. The work reads fairly chronologically but will at times go into tangents covering events which are not yet put into context. The problem is not serious, though, and does not affect the quality of the work.
This is the premier military history of the First Crusade, and its value cannot be overestimated. It certainly deserves to be on the shelf with R.C. Smail's classic "Crusading Warfare: 1097-1193" and Christopher Marshall's "Warfare in the Latin East: 1192-1291). Other valuable works, while not about the Crusades specifically, are France's other great work "Western Warfare in the Age of the Crusades", Maurice Keen's "Medieval Warfare: A History", Charles Oman's "The Art of Warfare in the Middle Ages", and especially J.F. Verbruggen's "The Art of Warfare in Western Europe during the Middle Ages from the Eighth Century". A number of other works about the First Crusade specifically are extremely valuable in that they cover far more than just the military aspect. See, for example, Thomas Asbridge's new "The First Crusade: A New History", Runciman's dated but still valuable "The First Crusade", and Jonathon Riley-Smith's "The Crusade and the Idea of Crusading". I don't agree with some of his ideas, but David Nicolle has written some valuable works such as "The First Crusade 1096-1099: Conquest of the Holy Land". There exists a large number of quality general histories of the Crusades as a whole. Anything by Riley-Smith is excellent. Without naming too many, Jean Richard's "The Crusades c. 1071-1291", Hans Eberhard Mayer's "The Crusades", and Robert Payne's "The Dream and the Tomb: A History of the Crusades" are all valuable resources as well.