But it's not music. As Alex Ross, the music critic of The New Yorker, says:
Today is his eightieth birthday, here are some appreciations and critiques. I side with George Benjamin:
...a rigorous compositional skill is coupled to an imagination of extraordinary aural refinement. Pli Selon Pli, Eclat/Multiples, the spectacularly inventive orchestral Notations, Explosante-Fixe - these are among the most beautiful works of our time. Boulez's music has a very distinctive flavour - a love of rare timbres and spicy harmonies, a supreme formal elegance and a passion for virtuosity and vehement energy. The polemics that periodically surround him obscure the intensely poetic source of his musical vision.
As I wrote a while back:
Boulez arrived in Paris from the provinces in 1942....As a Schoenbergian atonalist,...he...found himself dissatisfied with twelve-tone music as it was then practiced. He was bothered by the fact that Schoenberg had radicalized harmony but still treated rhythm and form in traditional, even hackneyed ways. So he began working toward the idea of “serialism,” in which durations, dynamics, and instrumental attacks were organized along the same principles that governed the twelve-tone series. He achieved a mode of writing that was, if nothing else, internally consistent....
Even in the fifties and sixties, as Boulez abandoned strict serialism and began to write in a more fluid, impressionist style, he remained a composer of vibration, activity, unrest. He set the profile of “modern music” as it is popularly conceived and as it is still widely practiced—a rapid sequence of jabbing gestures, like the squigglings of a seismograph.
What happened around 1900 is that classical music became -- and still is, for the most part -- an "inside game" for composers and music critics. So-called serious composers (barring Gershwin and a few other holdouts) began treating music as a pure exercise in notational innovation, as a technical challenge to performers, and as a way of "daring" audiences to be "open minded" (i.e., to tolerate nonsense). But the result isn't music, it's self-indulgent crap (there's no other word for it).