A first rate biography should include a good description of the important achievements of the subject, give a good sense of the subject's personality, provide the appropriate historic context in which to view the subject, be well written, and have good documentation. Westfall's biography of Newton is first-rate in all these dimensions. Newton is arguably the most important person in modern history. His work inaugurates both modern mathematics and modern physics. His achievements as a physicist set the pattern not only for physics but also for the other natural sciences. Newton's impact in larger culture extended also beyond the world of sciences. The historian of religion George Marsden wrote that Newton was the most important individual in the founding of the 18th century Enlightenment. Though Newton cannot be considered a member of that movement, his example of demonstrating universal natural laws understandable by human reason was immensely influential in European intellectual culture.
Westfall provides a detailed chronological account of Newton's life that covers all his major (and minor) achievements and is simply excellent at integrating the relevant historical background information. As Westfall writes, we regard Newton as a scientist and the emphasis in on Newton's career as a working scientist and mathematician. But, this is described very clearly within the context of late 17th century Europe. Westfall, for example, devotes ample pages to Newton's study of alchemy and theology. Since Newton spent a large fraction of his life working in these areas, it would be imposing an anachronistic perspective to minimize attention to these topics. Westfall is excellent at describing both the intellectual and social milieu in which Newton functioned. The sections detailing the history of mathematics and physics of Newton's important predecessors and contemporaries are first-rate, particularly his analysis of the impact of Descartes analytical geometry and mechanistic philosophy. His descriptions of 17th century Cambridge, with its concentration of pseudo-academic placemen, and of the generally patronage driven world of Caroline Britain are excellent. Never at Rest provides a vivid impression of the nature of scientific work in Newton's time. Westfall does not shirk from presenting complex mathematical and physical topics. These sections are tough going for those who don't recall a lot of math and physics but very worthwhile because they give an excellent sense of Newton's transforming effects on these disciplines.
Westfall delineates Newton's difficult personality very well and is fair in dealing with the numerous conflicts in which Newton became enmeshed, particularly the famous priority dispute with Leibnitz. Some of Newton's behavior is shown also to have stemmed from unexpected sources. Newton's theological researches led him to the conclusion that much accepted Christian theology is wrong and he had to conceal his Arianism and anti-Trinitarianism for much of his life. Some of Newton's achievements are shown as stemming from unexpected sources also. Westfall shows that Newton's alchemical researches, with their rather mystical element, probably contributed to freeing him from dogmatic mechanistic philosophy and facilitated his development of the idea of a universal, intrinsic gravitational force.
Newton is a fascinating figure and this biography will remain the standard for the foreseeable future.