It bugs me that this is considered by many to be the “principle” text of existentialism. I don't buy Sartre as being fully committed to what I think of as existentialism. For me, existentialism should be pragmatic. Sartre is way too concerned with philosophical difficulties to be pragmatic. The problem, as I see it, is that ontology by its very definition is metaphysics. By writing a work of ontology, is is implicitly writing a work of metaphysics.
I agree with him on a lot of points but I don't understand why he had to write a 800 page book about it. I go with Samuel Johnson, who proved appearances are the only thing that matter by stubbing his toe. That's a lot easier, and a lot more clear to the average person, than writing this huge book which regularly accidentally turns into metaphysics. Rorty is right: when you criticize metaphysics on its own terms and in its own language, you yourself become a metaphysicist. If common experience cannot show people that appearance is reality than 800 pages about it won't do it either, they will only find more to dispute. Another thing, this book is clearly the product of a leisurely, reflective society. I'm not sure so many of our emotions would be so reflective if we lived in a world where we rose at dawn, worked all day, and then fell asleep after dusk. But maybe I'm wrong about that. Someone had to think back then.
He is also totally subjectivist. I disagree with him completely about the tree falling in the woods question. It definitely does make a sound with or without a human witness. I don't think this is something that we can figure out through dialectic or logic, it is something we figure out through science. Sartre is totally wrong about this. That means that most of what he says is probably wrong as well, even though I am inclined to agree with him about certain things. The more I read of it, the more issues I have with this subjective approach.