This is a fine book, on the condition that it's put in a time-machine and sent back to the 1910s.
I consider myself oldschool because I still favor Mondrian and the American Abstract but I really had to struggle mightily against Kuspit's narrow-mindedness in order to finish the book. Although I agree with him on some of his conclusions about post-art, I am mostly terrified about how he gets there.
His almost religious enthusiasm, charming at first, gets very tiring towards the end of the book. All the mystical and repetitive talk of spirituality, transcendence, feelings, inner reality and the like starts to ring like a bad sermon after a while. It seems he has serious trouble with any intellectual/rational approach to art. His Freudian attack on a brilliant guy like Duchamp was bad enough, and he completely lost me when he reduced all modern art (including Mondrian and Malevich) to a "cult of the unconscious".