Just a superb piece of music. One of the first major pieces I would play to anyone to illustrate how wonderful modernist music was.
Without wanting to bring the tone down, I may be guilty of having fallen in love with Boulez after buying the Zappa record that he conducted as a teenager. That is a terrible, contemptuous, record (no more than Zappa's greatly overrated "serious" music deserved in my view, although I am still a big Zappa guy) and nobody comes out of it looking good, but it lodged the name in my head at a young age.