A good answer to the dreary Existentialists, Foucault moved the ball forward after they set it down. By the ball I mean, what the hell are we supposed to do with our circumstances when they are stripped of the fantasy that philosophy so rudely dismisses?
Trust me, you don't want to read Sartre and Camus and Nietzsche and just stop there.
Foucault is a good step forward afterwards, analyzing the way institutions, language, and norms shape and restrict our thinking by implying boundaries. Some of what he dissects is almost like a precursor to neuro-linguistic programming and embedded commands.
It's one of those books you read and, immediately after finishing, shudder at the thought of going through the world without being aware of some of these ideas. As Robert Greene said, power is amoral; it simply exists - so you might as well learn what you can about how it works rather than being blind to it or pretending it isn't real.