To my eyes, the book is essentially a fast overview of the last ten years of science, debate, important subjects, and noteworthy people in the aging research and longevity advocacy communities. A survey of the historical and mythological roots of present day attitudes serves as a springboard into a fast look at some of the important lines of medical research and development - SENS, tissue engineering, longevity genes, and so forth. Then it's off to observe the squawking of Malthusians and their resource-based objections to engineering greater human longevity, followed by a side-trip into philosophical discussions of longevity, and then a soujourn in the realm of economics to talk seriously about how the length of life shapes society.
100 Plus is, I think, a good book to give to the average fellow in the street who would be flattened and slain by the attempt to read Aubrey de Grey and Michael Rae's Ending Aging. That book is where the meat is - but 100 Plus is a Cliff's Notes for the current state and direction of longevity science and the advocacy community supporting it. That is a useful thing: a person reading 100 Plus will wind up in roughly the same place as a casual reader of the high points of Fight Aging!.
Video of Arrison presenting on this general set of topics at TEDx earlier this year has made its way to YouTube for those of us not in the neighborhood. Take a look: