In the end, assessments on decades are colored by personal experiences and the biggest events that took place during that decade. It's easy to say, for example, that "the 60s were about revolution" but in reality that was mostly just the late 60s, the early 60s looked a hell of a lot more like the 50s. But the 50s had some pretty pivotal civil rights battles that would culminate in the mid 60s... and the assessment on the 90s is just relating the US, as others pointed out, there was a whole lot of countries going through periods of instability and in some cases turmoil during the 90s, east Europe trying to restructure, western Europe trying to deal with economic unity post-cold war, Africa starting to come apart and things like Rwanda and the Ethiopian famine, Japan going through a depression, China going through a rethinking of what it's all about...
I went to middle and high school in the early-to-mid 00s, and even though a whole lot of crap happened during that time, it seemed just like a hollow time full of fear, not much in terms of cultural advancement. It sucked for me, even though the economy was doing okay. The 90s was a real high time for me, not just in terms of a golden age of kid's entertainment between video games, TV shows, and movies, but also because I had as many friends as you could ask for. Maybe the TV shows were better in the 80s, but you can't really argue that video games reached a golden age point, and the Disney renaissance would make an impact on movies for quite some time.
So when I hear it being called hollow or disoriented or lacking definition, it doesn't ring true to me, to me it seemed like it not only laid foundation for future technology and culture, but also did it well, at least where a kid might be standing. I might have a different perspective when I'm 80, but to me, the 90s were about hope and good times, the 00s were about fear, with everyone telling everyone else to be afraid, whether it being about sand people or the recession. So maybe the 90s sucked to a guy who went through the hellish gauntlet of high school during that time, but to me it could have very well been the best decade I can say I lived through the entirety of, which to be fair has only been 2 so far.