Having consumed most of the recent volumes on the life and times of our third president, I would have to say that Mayer's book is one of the strongest when it comes to the concrete exploration of his political thought processes.
One of the reviewers on the back cover copy says that "Mayer allows Jefferson to speak for himself. This alone would recommend the work." Indeed. This is one of the strengths of the book with its extensive referencing to the words of one of our founding fathers. It also does the same justice to the philosophers and statesmen who influenced Jefferson throughout his life.
One of the most interesting aspects of the book is the scholarly analysis of what it meant (to Jefferson) to be a Whig. I was also compelled by the discussion of the whig concept of a government is more republican (small r) if it is founded in jealousy, and not in confidence.
Mayer is not reluctant to point to many of Jefferson's overly optimistic or downright naive assumptions on the practical implications of running a government.
One area I wished Mayer spent more time exploring was Jefferson's thoughts on bicameralism and separation of powers; and more specifically on the original contention that the Senate served as a break on run away emotions protecting minority interests (to avoid tyranny of the majority that Madison was so fearful of, but not Jefferson).
All told, this book is of value for those who admire Jefferson, who are critical of his standing, and for those who quote his examples without really knowing what they are doing.