To me personally, it feels like Windows 2000 was the last and maybe only consistent UI onto which all later versions bolted what they considered improvements without ever overhauling the UI in full.
I think Windows XP did a pretty good job for the home market, making Windows appear friendly and easy to use to a wide audience (and without too many style inconstistencies).
Moreover, Windows XP let you switch the interface back to the classic 9x look, if you wanted a more serious appearance, and better performance.
We're both right. Windows XP had two different legacy themes: "Windows Standard" which looked like Windows 2000 and "Windows Classic" which looked like Windows 9x.
Yeah, but many of its 'advanced' settings and such still pop-up windows 95-styled interfaces. And these are actually the most user-friendly parts of the OS.
Moreover, Windows XP let you switch the interface back to the classic 9x look, if you wanted a more serious appearance, and better performance.