Existentialism
This is a very dry, complicated (at times, unnecessarily so), and long book. The text is filled with technical terms from Phenomenology (a small philosophical tradition that was created by Husserl in the twentieth century) that most readers will have an incredibly hard time understanding. It took me a whole summer to read this book, and I required a lengthy exgesis to follow the arguments. For those interested in Existentialism, but do not know much about modern philosophy or phenomenology, I suggest reading Sartre's "Existentialism and Human Emotions" instead.