I have to admit that I read this book in the summer between finishing high school and starting college - a time when I felt sure everything I'd been taught was irrelevant. When I read Nausea, I thought and acted like I had discovered the holy grail! I told all my friends (all 3 of them) they HAD to read it. I fell in love with this book with the intensity only a young person in their late teens can. (Evidently not all young people feel this way. My best friend still blames me ruining her summer by insisting that she read it.)
It isn't necessarily that the book revealed all the secrets of the universe to me, but it did start a whole summer of revelations. In the process of having to explain why I thought this book was so great I starting Thinking (capital "t" not a mistype) rationally and realizing that a sound argument is not merely a matter of volume, wit and "touches!" I read more Sartre and Simone de Beauvoir along with other modern philosophers. I also began establishing my philosophy.
Philosophy itself was a new concept to me. Not because I didn't know about it, but because I had a vague idea that philosophy had pretty much began and ended with the Greeks. OK, maybe I would even add St. Augustine - but by then I was already "outgrowing" the Catholic Church. I was primed for new ideas.
Am I an existentialist or a Marxist now? The only way I can answer that is that once one has completed 10 or so years beyond 19, experience teaches you that life is too complicated to be able to define yourself by one or two words that are loaded with dynamite. All that I feel sure about is that I still conciser myself a feminist and I still have enough optimism to call myself a liberal.
I do recommend this book - if for nothing else to challenge your ideas. If for you, as for me, it turns out to be the middle of a wheel with many spokes, you are in for a lot of research. I give it 4 stars for being challenging and thought-provoking.