Well obviously you cannot sum up the work of any thinker in 1 sentence. But Foucault is actually more of an historian than a philosopher & he provides excellent histories of how many notions that we usually hold to be natural or inevitable are circumstantial and were constructed surprisingly recently, and how the construction of these notions corresponds to the activities of power in our society.

Also probably some portion of his work has been itself naturalized and will seem less novel now that we all live in a world where many people have read Foucault.