Conversation so far:
What was Johns earliest work?
HPSCHD (1969), a gargantuan and long-running multimedia work made in collaboration with Lejaren Hiller, incorporated the mass superimposition of seven harpsichords playing.
Was it well received?
five-hour performance at the University of Illinois in 1969, in which the audience arrived after the piece had begun and left before it ended.

Question: Was anything unusual about it?
Self-contained rewrite: Was anything unusual about HPSCHD by John Cage?