Easier book of postmodern philosophy?

I am a college student who studies philosophy as a hobby but not with formal traing. I have some knowledge and read books by Plato, Aristotle, Hobbes, Mill, and some of the Enlightenment figures. I want to start to get to know postmodern philosophy, especially critical theory. However, most books of postmodern philosophy are very dense and difficult. What is a good beginners' book on postmodern philosophy?