If you want truly, truly heavy and thought-provoking you need to get away from brick-and-mortar bookstore, commercial, non-fiction, and get into work that's produced within and for academia.
For example, I've learned more from Anthony Giddens, Crawford Young, and Peter Berger in a handful of books than almost everything I've learned from pop books combined. The real stuff you want to read is in academia and fairly hidden from public view.
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