Win2K was the first one for which I've heard about it personally, probably because that's when it started to show up en masse in developed markets.
https://en.wikipedia.org/wiki/Microsoft_Product_Activation
Let's rephrase @endgame's comment as "Windows XP and Office XP were the first versions of their respective series where product activation was mandatory on all retail editions." Point still stands I guess.
8 gutted the Windows theme engine because most of it wasn't needed to render flat squares and it still has yet to recover.
Out of the box, the extra window title height took up too much room, ugh. But then now there's so much whitespace everywhere.
And one more click to disable the XP-style control panel.
OTOH app compatibility in XP was quite a bit better, esp. with games. IIRC that's when Windows first started to experiment with features like virtualized disk and registry writes?