This book is pleasantly dense with interesting ideas about what the future holds. The title refers to the progression of material-driven stages of human progress -- the Stone Age, the Bronze Age, etc. In "the Diamond Age", matter compilers can easily create diamonds out of raw carbon. Basic foodstuffs and many other material wants can be satisfied by these matter compilers. This has created a world in which no one need starve. However there are still tremendous disparities between rich and poor, because many human comforts such as entertainment and fine food still require the services of other people, which must be bought in hard currency. Networked nano-technology is all-pervasive, with microscopic robots putting these poorer citizens under constant surveillance. Faced with this hyperactive stew of technologies, ancient instincts and traditions run strong. Crime, poverty, and tribal conflict are still rampant in this world. People cling to old ways of thought (a strong Confucian motif runs through the book) to help make human sense of the rapidly changing world.
Against this backdrop, a fantastically advanced piece of technology (a sentient child's primer) is stolen, and winds up in the hands of a destitute young waif named Nell. Her resulting world-class education, and what she does with that education, is the binding for the various threads of the story.
The book's characters are well-realized for the most part, the writing style is honed and mature, the plot is intricate and engaging. The ending is controversial in its ambiguity, but that does not diminish the power of the book as a whole. In all, a very thought-provoking read.