I don't know much about Foucault. I 'read' (in a fashion), The Order of Things -- or at least some of it -- when I was a dumb kid, but didn't understand any of it. As in 'zilch'. But reading this 'dummies' book reminds me of a different experience I once had.
When I first read Lévi-Strauss, The Savage Mind, I was overwhelmed by it. It changed my life. The sheer intricacy of his mind, and the effort it took to read this book - remarkable in its intelligence and clarity -- simply bowled me over. It took quite a while, in fact -- a lot more Lévi-Strauss and some critical readings that infuriated me -- before I finally realized that the complexity masked a simplicity of thought (an ontology of binary oppositions) that was simply false. And that cured me, for all time, of modern French philosophy. A bit, when all is said and done, like Gertrude Stein's famous L.A. quote.
I very much doubt if now, in my doddering old age -- after spending literally decades reading Plato (with a fine tooth'd comb) -- that I'm likely to be more attracted to deconstruction, post-structuralism, post-modernism, post-etceteras -- whose fundamental epistemological claims are thoroughly refuted (there's nothing new under the sun -- in philosophy, at least -- as Whitehead said) by a careful examination of the Theaetetus and the Sophist.
At any rate, this book is very good, brief, but balanced -- and an excellent and clear introduction to the work of a very difficult writer.