A refreshing investigation into Foucault's genealogy, which makes Foucault much more revolutionary than other commentators I have read make him seem like. This review consists of two parts that are (I believe) most important in this book.
1. Genealogy as problematization (vs Nietzsche, vs Bernand Williams) and its relation to Kantian critique
While Nietzsche's use of genealogy is subversive, i.e. he traces the immoral emergence of slave morality to subvert this value system, and Bernand Williams' use of genealogy is vindicative, Foucault's geneaology is problematizing. This means that Foucault's genealogy, as opposed to Nietzsche and Williams', is not strictly normative. Foucault's genealogy traces the history of an idea to expose certain contemporary problems that we haven't thought about before. Foucault opens the questions, not closes them (like Nietzsche and Williams). The benefits of doing this, instead of a strict normativity, is that it could avoid the genetic fallacy that Nietzsche and Williams often come under.
Koopman also argues that Foucault is a Kantian, with regard to his critique. Like Kant, Foucault also used critique to sketch out the limits of our thoughts. The similarity ends there, however. Foucault's method is historical, while Kant's is transcendental, and this results in the fact that KAnt's critique aims to make sure we don't cross the transcendental lines to make some unsubstantiated conclusions about the world in itself, whereas Foucault's critique aims at the opposite: to transcend those historically contingent limits, and to allow us to think in a radically free way.
2. Genealogy as an addition to archaeology
A criticism of archaeology is that it freezes time and doesn't account for the changes between different systems of thought. Genealogy remedies this, by analyzing multiple vectors (power-knowledge) so when one vector changes, the other does, and this leads to historical changes. So genealogy provides us not with the contingency of our system of thoughts, but also how we came to be in this particular discursive structure. It provides us with ample material, the tool by which we can transform our way of living.