It was also the first year the Grammys even had a Hard Rock/Metal award, introduced in part because of the landmark releases a few years earlier by metal bands (remember that Peace Sells... But Who's Buying?, Reign in Blood, and Master of Puppets all came out within six months of each other) that finally legitimized the genre in the Academy's eyes to offer the award.
....which they then promptly gave to Jethro Tull.
SZA's album CTRL was my personal pick for best R&B album, especially since 24K Magic is only barely an R&B album in the first place.