Music Man

I was having a discussion the other day about what constitutes a great piece of art - music specifically.  And my take was that it was something about which you could say "After this, nothing was ever the same again". Three examples -  Beethoven's 6th symphony - the symphony as programme music, never been done before. Stravinsky's "The Rite of Spring" which opened the door to dissonance.  And Tchaikovsky's 6th symphony which ripped the format apart and rewrote it as an emotional tour de force.  What do you think?