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.
Was anything unusual about it?
with fifty-two tapes of computer-generated sounds, 6,400 slides of designs, many supplied by NASA, and shown from sixty-four slide projectors, with forty motion-picture films.
Did it have unusual rhythmic structure?
CANNOTANSWER.
Where there any special artists involved?
excerpts from the works of Cage, Hiller, and a potted history of canonical classics.

Question: Did he have other early works?
Self-contained rewrite: Aside from HPSCHD, did John Cage have other early works?