I think Cage is pretty neat in his ability to make us look at music completely differently. Who are we to say that "silence" (which turns out not to be silence afterall) is not music? Afterall, in a full concert hall, without music occuring--but still with a focus onstage--there will invariably be an extraordinarily complex collective "improvisation" from the audience, supremely spontaneous in design and conception. What's more--and this is related to the sound--it explores a certain awkward emotion which is not ever unearthed in music another way, that is, the uncomfortability of grand silence in the presence of others. People will be tempted to talk and move about to clear the feeling, and as time grows on they will grow even more restless, all on account of the musician on the stage, who by that point would have a remarkable command over them.
His sonatas and interludes for prepared piano are also, believe it or not, worth checking into. They have the neat result of becoming, as he said, percussion ensembles for a single person.
The general consensus, however, amongst supporters of Cage, is that we like him not as a musical composer but as a musical philosopher who tends to challenge how we think of normality and expectation and what we can do to oppose such things.
Topic: John Cage: What is the name of this stuff?