Before I used YouTube to determine that the last great rock band was Guns N' Roses. However, it might be more helpful to appreciate how much better or worse the musical zeitgeist is by ignoring the top-rated groups, since the presence of superstars owes more to chance than does the presence of pretty-good-stars. Think of it another way: in between the best songs on the radio on a typical day, what do the next-best filler songs sound like? As I mentioned when looking at commercials, we often take the mundane for granted and forget how good it was only once we've lost it -- or if it was bad, we look back only later on and thank god we don't have such terrible filler material in our pop culture meals.
Obviously if the best music of today sucks, the groups from the 50th to 90th percentiles are even worse. Just turn on the radio and hear for yourself what the filler sounds like. (I'm putting aside the three years of good music in the mid-2000s when rock saw a new wave revival and crunk finally made hip-hop music fun and danceable again after over a decade of gangsta rap.)
To be as fair as possible, for the pre-'90s death of rock music, let's look toward the very end when it was on its last legs. Let's also restrict it to groups who weren't superstars, and even then look only at their third or fourth most famous hits.
"In Your Room" by The Bangles
"Don't Look Back" by Fine Young Cannibals
"Dressed for Success" by Roxette
I know, I know! But truly, even this low standard discovers much better music than what the highest standard would among today's whiners and warblers. It's not too hard -- all your song needs is the presence, rather than the absence, of melody and a fun vibe. And how girly are The Bangles compared to The Spice Girls or The Pussycat Dolls! Susanna Hoffs sure is a sight for sore eyes (not to mention the bonus points she gets for being born in the disco-punk generation). Even the masculine chick from Roxette is soft and cheery compared to later hard rockers like Courtney Love, while still rising above the fair sex's penchant for sappy navel-gazing a la Ani DiFranco or Norah Jones.
We haven't enjoyed any good new pop music for nearly 20 years, but on the bright side, popular recognition of this seems to be mounting. This means that, rather than enjoying old music only on your own, you can get the extra rush from knowing that it's in the air and fashionable. It would be nice if human happiness didn't respond to that, but it does. Where it exists, '80s night is incredibly more popular among young people than nights that feature music from the past 10 or even 20 years. If you drive around with emo or Jason Mraz blasting out your windows, most people will shoot you nasty looks for polluting the air.
But change it to The Go-Go's or Prince, and see how many genuine smiles you'll produce (and no mean glares). That's not just for older people for whom there's nostalgia value -- even people who were toddlers during new wave, or even those who weren't born for another 10 years, get a kick out of it. Good is good. It's like going into someone's house and seeing pre-Abstract Expressionist art on the wall, or going through high school in one of those Collegiate Gothic buildings rather than in a concrete and glass box.