Well although I agree the music from the 60s, 70s, and 80s were amazing I don't think we can exclude everything out yet. There was some amazing music in the 90s and still some decent ones in the 00s. I just think with the enlargement of mass media, expanded basic cable, and the internet people are kinda drowned out by some music and even the music is drowned out. Music becomes more about the visual rather than the audio which quite ironic. It's no longer just about hearing music but seeing it as well. I think that has caused music, mainly pop, rap, and country to really become irrelevant in timeless great music.
However, I'd say in things that don't fit those categories, the music has stayed amazing. Look to the 90s for some great alternative rock and even nowadays. Grunge music was simply incredible in the 90s and unfortunately some untimely deaths killed it before its prime. Nirvana, Stone Temple Pilots, Pearl Jam, Alice in Chains, Soundgarden, etc all brought some music that defined the 90s. Also had bands like Green Day, Radiohead, U2, etc all had great hits. I think these bands with their songs from the 90s and even some from the 00s will become some of the classic music we talk about for decades to come.
When we get to the 00s it's a little bit harder to figure out but there have definitely been some great artists such as Muse, Shinedown, etc. Maybe if we can get past the drowned out music we can look to that of alternative rock and music genres which have thrived during it.