This is the best book I have ever read on Foucault, no contest--though one must be clear that Halperin is EXPLICITLY NOT attempting any general and comprehensive explanation of Foucault's life work and thought, which Halperin makes quite clear, though there seems to be some confusion below regarding this point. In fact, the tone of some of the reviews only serve as a demonstration of some of Halperin's points.
My main criticism is that I would go even a little further than Halperin with respect to Foucault's actual purpose or mission in _The History of Sexuality_. I would say that, with volumes two and three, Foucault has shifted his purpose from a general "history" (hence the title) of the rise of "sexuality" to a deconstructive and very narrow focus on certain discourses in antiquity that ostensibly SEEM to mirror our own while actually being quite alien to it. It just so happens that these ancient discourses are about men. From this perspective, all the complaining of a small but very loud minority of feminists merely reflects a failure to understand what Foucault was doing. He wasn't trying to give us a general history; rather, he became fascinated by how the ancient world's most familiar discourses (which are about men) could, in fact, be extremely different, by the demonstration and analysis of that difference. As for general history, Foucault repeatedly refers the reader to Dover's _Greek Homosexuality_, which was published between volumes one and two, and which he just as repeatedly tells us he accepts in basic outline. Feeling there was no longer an urgent need for a "history," he gave us his actual second and third volumes. Should he have given us a hint he was changing course? He did!--in the introduction of the second volume. Readers need to learn to be a bit more active--though, clearly, as original, good, and rigorous as the thinking and analysis may be, it does make for a rather uniquely structured set of books.