Cambridge Music Handbooks - Nicholas Cook, Cambridge University Press (24 June 1993) - "Beethoven's Ninth Symphony is acknowledged as one of the supreme masterpieces of the Western tradition. More than any other musical work it has become an international symbol of unity and affirmation."
It is also the first musical piece ever added to the UN World Heritage list.
In 200 years no one will know what "Teen Spirit" or "Hotel California" even was. But they will still be playing Beethoven, and Mozart, and Bach, etc... Even today, 15 years later "Grunge" is almost a forgotten fad. And that's kind of the point. How can it be that important if it doesn't even have staying power for two decades.
Kids today are playing Pink Floyd, the Eagles and Led Zeppelin but I never hear Nirvana.
Don't get me wrong, I like Teen Spirit, Hotel California and all the rest - I just have a hard time calling them "important".