A sad book, a mind-opening book, and many more things. Viewing these photographs will conjure up completely different personal reactions, depending upon your frame of mind at the time of viewing. That is what is so remarkable about Arbus' work; so many emotions are brought to the surface.
And while I know that some people will be turned off, even repulsed by this final phase of Arbus' work, I strongly disagree with the reviewer from Chico, CA in saying that it would have been better if this work has not been published. This work is not pretty, and it is not candy-coated, but it should be, and thankfully has been, published. Real life is not always pretty, and we each have our own concepts of such ideals. If you are uncomfortable with other's perspectives on beauty and reality, close the book or sell it to someone else. But do not impose your censorship on me.