Professor Frick said:
The problem for rock in the 90s is that it is so heavily front loaded with good stuff up to about 96, but the second half of the 90s was by and large terrible. By that point the 'alternative' sound had just become a copy of a copy of a copy. There were certainly some great albums in the second half of the 90s, but for every 'OK Computer', there were 4-5 'My Own Prisons'.
Easily solution to this, and it's what I was going to say anyway.
86-95. Why? (I've included mostly rock, but some landmark albums of other genres as well)
1986 - Master of Puppets, peace sells, reign in blood, slippery when wet, graceland, true blue, invisible touch
1987 - joshua tree, Bad, appetite, permanent vacation, document, kick, faith, cloud nine, whitney, ocean front property, always and forever
1988 - operation mindcrime, straight outta compton, and justice for all, rattle and hum, wilburys, open up and say ahh, skid row, money for nothing, journey greatest hits, fleetwood mac greatest hits
1989 - like a prayer, full moon fever, Garth, batman, pauls boutique, dr. feelgood, Pump, pretty hate machine, flying in a blue dream
1990 - shake your money maker, violator, mariah, mother love bone, cowboys from hell, facelift, to the extreme, hammer don't hurt em, rust in peace, seasons in abyss, immaculate collection, no fences, livin it up
And then grunge and 90s alternative (and the black album) took over, along with more landmarks in hip hop/rap/pop like dre, snoop, big, tupac, beasties, en vogue, tlc, mariah, etc., so I don't have to list 1991-1995. It leaves out the late 90s which was good at the time, but much of it hasn't held up. It all stemmed from its better early 90s predecessors.
That's a pretty good 10 year span. It includes classic metal, classic 80s/arena rock, classic grunge/alternative, classic hip hop and pop, and a few country landmarks, including the arrival of Garth and 90s country.
That's a lot of 'classic'. No other 10 year span on this board so far has that many classic varieties/genres.