Because of the hard-to-pin-down nature of Foucault's notion of "power," I often find myself sympathetic to the following criticism of Foucault even though overall I admire the guy like crazy:
"Frank Lentrichia notes that power, in Foucault's social theory, ' tends to occupy that "anonymous" place which classical treatises in metaphysics reserved for substance: without location, identity, or boundaries, it is everywhere and nowhere at the same time. It resembles in its ubiquity the God of theism. Unlike that God, however, it has 'no predominant direction, no predominant point of departure, no predominant point of terminus.' Indeed, in its imperviousness it resembles 'some Eastern metaphysical force that ensares us all.'"
-Allan Megill's Prophets of Extremity: Nietzsche, Heidegger, Foucault, Derrida, p. 240, University of California Press
I bet you can find a passage that contradicts this. And another that buttresses its salient point. And on and on. Foucault's ever-evolving notion of "power" and his sometimes frustrating ways of deflecting direct questions about it -- by asking other questions obliquely related, instead of providing hard and fast answers -- can try the patience, and I suspect a good many people think he had The Key somewhere in all his rhetoric. Maybe he did! His lectures at the end of the 70s in some ways validate Sahlins' comparison to Hobbes -- he apparently began to conceive of social relations as merely war in variegated forms. (So did William S. Burroughs, who said we live "in a war universe. War all the time.")
I'm not sure that is unamenable to leftist analysis, however. Nor is the notion of will-to-power, which does not necessarily imply violent force or coercion, but can in fact also mean something like self-actualization.
Having said all this, learning about "power," I've found, is not something one can do with Foucault and Foucault only, despite what experts on The Master and card carrying members of the Fou-Cult might suggest. Bertrand Russell's _Power_ and even Michael Mann's _Anatomy of Power_ &c. (and of course Marx and 'd argue a LOT of the anarchist tradition, which unfortunately usually gets ignored despite the tremendous wisdom in much of it) are vital to forming a comprehensive whole.
-B.