Definitely a Must to understand Mongolia and its history. The book was written in 1961, 40 years after the "independence" and it portraits the unique case of a herder's society and its transformation in a socialist republic. If you match this book with Rossabi's "Modern Mongolia" you get an insight of the amazing transformations occurred in this country in the twentieth century.
Lattimore is a scrupulous researches and it's a pleasure to read his account.
I was particularly interested in the account of the role of Buddhism in the feudal system.