This is a provocative and important book, maybe even pivotal. Bent Flyvbjerg says that he's arguing for a new approach to social science, but I think his thesis is considerably more radical than that: he's effectively calling for social "science" to be abandoned and instead replaced with a sort of applied social practice analogous to medicine and civil engineering, endeavors which draw on science but necessarily go well beyond it.
Flyvbjerg begins by arguing that social science never has been, and probably never will be, explanatory and predictive in the way that the natural sciences are, especially the physical sciences. A main reason is that context and judgment are key to any kind of practical social science, yet they can't be reduced to theoretical terms. The arguments here borrow from the critique of AI presented by Hubert and Stuart Dreyfus.
These limitations are fatal flaws for the project of social science modeled on natural science, so Flyvbjerg instead revisits Aristotle's classification of "intellectual virtues" and argues that, rather than aspiring for the virtues of episteme (associated with science) or techne (associated with technology), social science is better associated with phronesis, which is concerned with practical action in particular human situations, and thus deliberately and reflexively brings in context and judgment, along with considerations of values and interests. And because particularities are so important in making practical judgments and decisions, high-quality case studies are an important tool for phronetic social science.
The one element Flyvbjerg finds missing in Aristotle's conception of phronesis is explicit consideration of the issue of power, and he explores the ideas of Habermas, Nietzsche, and Foucault to help redress this. He finds Habermas' aims to be laudable, but his approach to be ultimately idealistic to the point of being infeasible. Nietzsche and Foucault turn out to be of greater value, largely because of their emphasis on contextualizing genealogical analysis.
Flyvbjerg next distills a set of methodological guidelines associated with his phronetic social science framework, and finally illustrates the framework with an interesting case study involving city planning (his specialty) in Denmark.
I greatly enjoyed this book, surely in large part because I tend to agree with Flyvbjerg's thesis and reasoning, and I guess it's not a coincidence that the philosophers he draws on are among my favorites. I also found the book to be well written and smoothly translated from the original Danish, though the chapters related to power were somewhat tough going at times.
Overall, I highly recommend this book to anyone with a serious interest in social science. However, at least a modest background in both social science and philosophy are probably prerequisites, since this is a fairly sophisticated book aimed more at an academic audience rather than the general reader.