Foucault is sufficiently clear, especially as far as the French academy goes. Read Derrida's "Glas" some time for comparison as to what actually constitutes academic obscurantism (the book is literally untranslatable, but doesn't make much more sense in French). Foucault's lectures are less technical than the books, by the way.
Sheridan's Will to Truth or Merquior's Foucault monograph are probably the most concise and obvious treatises if you are unable to simply understand what the man is saying. If you've read Nietzsche's Genealogy of Morals and Foucault's own Archaeology of Knowledge - at minimum, his genealogical project should be fairly obvious. Deleuze's Foucault monograph is also fairly good, if overly entrenched in French academia and a bit fawning (they were close friends in real life).