I know virtually nothing about military campaigns - and less about history in general than I'd like - but this book was excellent. It made things clear without being condescending, and the before/after maps and summaries were great. My interest in the subject is for the purpose of writing fantasy, so I especially appreciated the way each battle profile was chosen to emphasize the importance of one factor, such as "smart leadership" or "underestimating the enemy," that could be generalized to other (read: fictional) battles.
The book uses a number of historical battles to show how, for example, surprise or underestimation of the enemy can play a role in the outcome of a battle. The text first sketches the overall situation, next shows how the plan was supposed to work, followed by what actually took place.