i'd check out the tape-phase pieces from the sixties, "It's Gonna Rain",
"Come Out". "Violin Phase".
"Music for 13 Musicians" is a good example of his 'classic' instrumental
ensemble sound. (If you haven't checked out Terry Riley's "In C" you
oughta, it spawned this whole trip).
I can't stand some of the later stuff, especially the dialogue-driven "The
Cave".
k