There is a gap between every budding generation and rock music / music is no exception being it a cultural form of art.
Having said this, I think first we have to define "good music"; in my opinion, good music is any music which is not exquisitely 100% commercial , in other words, music that is not created to fulfill the latest fad no matter what, thus disrupting the truly artistic vein of the artist who produces it.
For example, Michael Jackson sold millions and millions of records, but that doesn't necessarily and automatically make it good music.......same thing goes for Kiss, Queen, Bruce Springsteen, Journey, Donna Summer, Eminem, just to mention some over the whole spectrum. There is so much overlooked music out there, it's not funny anymore.
Musically speaking, Don Costa, the greatest arranger of music, once said "the big diff between a good song and a mediocre one is to be found in the arrangements". He was damn right.