In summary, Armstrong's "Buddha" is a brief, sympathetic account of the life of the Buddha in the context of his time. It is marred by brevity and by a distanced, clinical treatment of the Buddha's dhamma that makes it seem little more than an antique, cultural artifact, not a relevant way of life.
I am guessing that the format for the Penguin "Lives" series accounts for some of the shortcomings of this book including: its brief length (less than 200 rather small pages); its lack of illustrations; its rather abrupt end with the Buddha's death (not a word of how one teacher's words grew into a worldwide religion); the absence of a guide to the pronunciation of the many Pali terms; and the omission of an index.
These lacks show the book is not intended as a definitive biography; nor it is it intended to have theological depth that would challenge a well-read Buddhist. This is a popular "life" intended to give a broad picture of the Buddha's life and dhamma to a curious non-Buddhist reader or to a student.
Within the scope of this limited goal Armstrong has done a reasonably good job. Certainly it could not have been easy to shape a conventional, biographical tale from the Pali canon and other Buddhist scriptures. Armstrong stresses that an integral part of the Buddha's teaching was the unimportance of the ego, and for that reason the Buddha's personal attributes virtually disappeared, both from his teachings and from his disciple's accounts. Little is left but the suttas themselves, and some highly-colored legends surrounding the key moments of the Buddha's life.
Armstrong is particularly good at taking the legends and drawing out their inner meaning. She recounts a legend sympathetically; then shows how it make clear sense, not as history but as a statement of belief in the context of the time, or as an archetypal portrait of the human condition. For example, she notes how Mara, Lord of Illusion, "rpepresents ... all the unconscious elements within the psyche which fight against our liberation."
In large measure Armstrong explains the Buddha's dhamma clearly and sympathetically. Yet she always seems to handle it with metaphorical tongs, like an interesting specimen -- not as if it were a living tradition the reader might enter. Part of this impression comes from her consistent use of the perfect tense when describing the dhamma. For example, she writes "The purpose of both mindfulness and the immeasurables was to neutralize the power of that egotism that limits human potential." In this and many similar sentences, she uses the perfect ("was") or the conditional ("would"), as if the dhamma was a teaching that existed only long ago and among distant people. There is no hint that mindfulness IS used for the same purpose by people today.
This is a subtle matter of diction and tone; but its effect is to transmit an unspoken message that Armstrong herself has not entered into the Dhamma, and probably wouldn't care to recommend it to her reader, either. If you think of yourself as being in some degree "buddhist" you may find this air of faint praise makes you uncomfortable.
A less subtle problem is Armstrong's repeated insistence that the Dhamma "could not be understood by rational thinking alone. It only revealed its true significance when it was apprehended 'directly,' according to yogic methods, and in the right ethical context." By "yogic methods" she means the disciplines of mindfulness and meditation. By "ethical context" she means principly the practice of metta, empathy.
Armstrong seems sure that the dhamma is not capable of being defended or supported by discursive argument. Or at any rate, she does not even attempt to sketch its philosophical underpinnings. This is strange. Armstrong is certainly capable of dealing with abstracts and logical argument. And Buddhism is quite respectable as a philosophy, as coherent and complete in its account of the universe and the human condition as anything produced by Plato or Aquinas. Armstrong completely neglects this aspect of the dhamma, leaving the impression that it can only be entered through "yogic methods." In short, she writes as if the dhamma is unapproachable unless you are ready to enter into dubious Eastern practices.
Karen Armstrong has made quite a career out of writing biographies, not only about manifestations of the divine, but the early history of the movements they inspire. If the potential reader is looking for esoteric tracts on yogic practice (and the Buddha would have abhorred such fascination) then this is not the book they need.
Rather, this delicious and brief treat of a book explains what Buddha and Buddhism meant in the context of their early history. India had become a place where great business republics were involved in rapid economic growth (like today's global economy) and were being consumed by the new monarchical states. A huge middle class was emerging that could not be pigeonholed into the old caste system, and therefore rejected it; life had become overly materialistic and people were desperately turning to anything for a sense of spiritual well-being (sort of like today.)
What Armstrong does simply and wonderfully is reveal this worldwide phase of history and the contribution of the Buddha in meeting its challenges. His teachings are decidedly NOT the mysterious, esoteric bunk that priesthoods of every religion have invented to maintain their exhalted position, but were in fact very practical means for bringing the unhappy people of the age into enlightenment-- sort of like what people are looking for today.
I was especially happy to read this book because of these larger, "global" contexts that are expressed or implied. Buddhism belongs in the hall of great world religions, as Buddha belongs among the great manifestations of the divine. Armstrong has delivered a fine portrait of the Buddha's life that puts them both in their proper place, yet she avoids the trap of making them such objects of adoration that the text would become a mere tract.
I sincerely hope that Karen Armstrong will see fit to examine other religions and manifestations like this. I would particularly like to read anything she has to say about Zoroaster or Baha'u'llah.