13th of 20, roughly by chronology.
I'm up to 1975 now, which means punk is beginning to rear its head. Patti Smith is not only the first punk artist on my list, she was the first punk artist we saw live, in 1976. (It occurs to me that we saw all of the last 8 artists on the list in concert, at least once and often more than once. The joys of being an adult with a coupla bucks in your pocket.) More than half of the remaining albums are punk, or rooted in punk. This emphasis (some would say, over-emphasis) on punk means a couple of powerful genres won't make my list. Disco never struck me as an album-oriented art, so that's not a big loss (if you need some disco for the soundtrack, play "Don't Leave Me This Way" by Thelma Houston). And hip-hop disappears under the punk onslaught (the last two hip-hop albums I cut were It Takes a Nation of Millions to Hold Us Back, and Paul's Boutique). I've made it this far without saying anything about why Horses matters so much to me. Perhaps the accompanying video, which features a couple of songs from Horses being performed 40 years down the road, helps explain it.