In addition to pitch, dynamics, durations, articulations, and instrument entrances are all serialized. Extremely complex, conductor needed for even small ensembles. The music is meant to be experienced, not understood.
WT: "Who Cares if you Listen"- music as evolution, scientific discovery. It has to happen regardless of people listening. More efficient tonal vocabulary. Forces people to improve their perceptual capacities.
Peter Boulez Le Marteau Sans Maitre 1955