Odd as it is, I think 4’33" is one of the most important pieces of music ever performed because it changed conventional ideas of what is and is not music. I’ve never heard it because I haven’t had a chance to hear it live and I won’t listen to a recording. I don’t think it was ever intended to be listened to on recording, since Cage thought every performance of music is different.
Many people believe that rests are the most important notes in music - they hold most of the music’s emotion and intensity. 4’33" is just an elongated rest.
Not everyone considers it music, but then, I don’t really consider Britney Spears music… to each his/her own 