This is a composer who's ideas were better than his music in my opinion. Schoenberg described him as "the inventor of genius" and I firmly aggree with him. A lot can be learned from Cageian ideas about the nature of music and how we respond to music.
Although quite a bit of his music is lacking in artistic merit (such as his radio music), his works for musicians can be very liberating. I went to hear his piano concerto recently and there were points during the performance where the orchestral players could make any sound they wanted. Also the piano part is a graphic score which I find very exiting as it closes the divide between composer and performer (the performer being free to semi-compose the work themselves).
John Cage I understand is a cotravertial figure and I know how we all like that so let battle commence!