I arrived ca. 2001 and found enough high-quality content (folk songs, math puzzles, some books already digitized) to feel like I had discovered a giant library. And it kept growing: Wikipedia arrived, various forums and magazines appeared (most were crap, of course, but there was no shortage of good ones).
As far as I can tell, things started getting worse around 2008, with places such as geocities closing down and social networks rising; then the deprecation of Java and Flash kicked the floor out of some of the good old parts. Other things were still improving, though, up to 2015 or so. It's only recently that I see most "culture production" locked in perennial closed gardens with unaccountable moderation. I wish I could point to some places still on the rise other than arXiv and LibGen...
What had I missed from the 90s that didn't make it into the 00s?