Fief: A Look at Medieval Society from Its Lower Rungs by Lisa J. Steele provides an excellent overview of historical Norman manorial society in the Middle Ages. The material covers England and northern France, and mentions Norman Sicily as well, from roughly the 10th to 14th centuries. The author touches upon nearly every subject from defining the Three Orders to agriculture and architecture through governance, society, the parish, and even warfare.
Where Ms. Steele hits her material with appreciable breadth, she doesn't penetrate too deeply into any one subject. The introduction states the book is a "primer on medieval life for fantasy gamers, SCA enthusiasts, and others interested in knowing what made society tick in the days of crusading knights and the Black Plague." That accurately describes the content of the book. For those who have never shown an interest in looking at the actual historical framework that D&D assumes, this is an amazing introduction to the material. For those looking for deep analysis, usable figures, and concrete game material, this book would require further research and work.
For example, there are price lists for common items, fines and fees for transgressions of manorial laws, and even upkeep fees for knights attending tournaments. However, the numbers are mostly presented as is, without explanation as to why prices can widely vary (up to a factor of 10) between certain years. It is certainly good fodder to work with, but nothing that can be used as is.
Personally, the material provides good reinforcement for what I already know. The time period and location depicted are outside of the scope of my Early Modern Period campaign. Yet, manorialism was still strong in the Holy Roman Empire at the time my campaign is set. So the material is still pertinent.