Considering yourself a music fan and not branching out to music before 2000 is...
Well, you're not really a proper music fan.
Anyways, here's my list... in case anyone needs ideas or older music to get into.
1 Portishead - Dummy
2 Boards Of Canada - Music Has The Right To Children
3 My Bloody Valentine - Loveless
4 Massive Attack - Mezzanine
5 Bjork - Homogenic
6 Sheryl Crow - Tuesday Night Music Club
7 Kate Bush - Hounds Of Love
8 Cyndi Lauper - She's So Unusual
9 Aphex Twin - Selected Ambient Works
10 Bob Dylan - Blonde On Blonde
11 Joni Mitchell - Blue
12 Madonna - Ray Of Light
13 Radiohead - The Bends
14 Fleetwood Mac - Rumors
15 Pink Floyd - Dark Side Of The Moon
16 Oasis - What's The Story Morning Glory
17 No Doubt - Tragic Kingdom
18 Steve Miller Band - Fly Like An Eagle
19 Madonna - Like A Prayer
20 Depeche Mode - Music For The Masses
Lots of 90s, granted I'm not that old and also took awhile to get into a lot of these artists.
Also, definitely not actually in order of my preference, but some of these need high rankings or they'll fail to chart.