I initially queried why I believed OR preceived that pre-early-70's music was better. I think in some ways music is like language, and the most powerful music for us may always be the music of our youth. Just as it is gets more difficult to learn new languages with age; it is harder to appreciate new genres of music as you get older.
Someone mentioned System of a Down - which is my 13 year olds favorite band. My 15 year old worships Aphex Twin and Moby. After years of dismissing them (if only because I thought my tastes should be more sophisticated than my kids!) I now grudgingly admit that they have some merit. But it has taken time. (I don't have unlimited time like JL). Like HUNSUCKER says, there is so much crap assailing our ears that I tend to tune most new stuff out and wait a few decades until the cream gets sorted out before I seriously invest my listening time. The problem with this approach is missing the opportunity to see the good stuff live. (I missed the first ten years of the Dave Mathews Band for this reason, but luckily they are still touring!)
In any event, even putting asisde the foregoing, I still think the last 30 years or so have been a relatively dry spell for music in general. I don't subscribe to the view that music is merely "sound in time." If it doesn't SING - it ain't music.