I tend to split the 90s music into three phases, because they each feel different to me.
1990-1992 -- mostly a fresh feeling to music from this era, as compared to the late 80s. Music feels sometimes controversial, and pushing the boundaries of societal norms. Generally feels scene-like... be it, the rave-scenes... the homo-friendly-scenes... the depressed-kids-scenes... the drug-popularity-scenes...
1993-1997 -- this is quite a comfortable phase for 90s music. The fresh and controversial feelings have gone now, and most popular music from this time feels very innocent and light hearted.
1998-2000 -- build up to the millennium. The music from this phase feels quite optimistic, and there is more dance/celebration type music. Synthetic and computer generated music feels quite advanced now. The distinct sounds of sample keyboards from earlier years have now been completely replaced with computer generated sounds, which are much more complexly arranged. The innocence and light hearted feel is now gone. Music now feels more serious and constructed, or at least, it feels like it has been created more mindfully and impersonally, unlike the music in earlier years.
Well said!
I do the same thing with the 80s...the early 80s I think of the punk and ska stuff, the middle I think of the pop Duran Duran British stuff and the end of the 80s is flavored by Bon Jovi type stuff.
The funny thing is, I feel those phases of 90s music have coincided with personal moments for me in the 90s. I see those phases as follows:
The early phase (1990-92) - essentially a hangover period from the 80s where the decade is still trying to find its unique voice. Music was essentially similar to the 80s with added synthetic beats and dance vibes. The Madchester scene's seeds were flourishing by now, and continued to do so, while old-skool house begat modern techno. These forms essentially dominated the charts for a bit. I believe there was even an attempt at a late-70s revival in terms of fashion and things - flares were everywhere again. And of course there was old-skool rap.

Me, I was finishing primary school by then, so the music scenes were reminiscent of the older times.
The middle phase (about 1993-97) was where we began to see 90s music take form. Initially there was the "Ragga" craze which was extremely popular in 1993, while rock became sullen and moody of note. The British indie scene would sprout Britpop, popular rock and dance music with a wry nod to the music of the 60s and 70s (especially Oasis and Blur, their sounds harking back to those of the Beatles/Stones and the Kinks respectively), even leading to a revival of the Beatles. Hip independent movies like "Trainspotting" and the like also saw a 70s music revival in general. Things were bright and breezy, but with a generally unspoken dissatisfaction over the way things were (John Major was in power, remember?) and a longing for things "new" and "cool" (this Tony Blair fella). Me, I had just reached secondary school by then, and had found my "own" voice as it were. They were great days, overall, though.
The later "decline" years: 1997 to 1999. The britpop dream was dying with the onset of New Labour reaching government and everyone growing wise to the politics of Blair and co, though the dying years were still overseen by established acts like The Verve, Manics and Blur, later to be taken over by more broader-appeal acts like Coldplay and Travis. Pop made a major comeback especially in 1998, wth the Spice Girls leading the charge since 1996. I believe there was even an ABBA revival by this time, later manifesting in the hit musical "Mamma Mia!" storming the West End. Rap, hip-hop and "RnB" (essentially souped-up soul with a hip-hop beat) and increasingly electronic processed sounds (see Radiohead), especially in the popular "trance" subgenre of dance music by decade's end, became increasingly attractive, and a signpost for the music trends of the 2000s. By this time I had hit University, and things were looking towards the future, an uncertain one in many ways.