XP and especially Vista looked sillier, with the constant need to update the UI to entice users to upgrade, but I think they
did actually improve technically, "under the hood". And by the time we got the best Windows ever -- i.e, Windows 7 -- I couldn't even tell you what that looked like natively[1], because by then I was in the habit of installing Powertoys and using its TweakUI component to switch to a W2K theme[2] the first thing I did with any new Windows installation I got.
Versions 8 and 10 may be even better, engineering-wise -- 10 certainly crashes or hangs even less frequently than 7 -- but since they won't let you you fix the crappy GUI any more, their usability suffers much more than the increased stability can compensate for.
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[1]: Pretty much like Vista, with that super-annoying "Glass"(?) transparency bumf as default... I think.
[2]: This, too, was whittled down over time. In XP, and I think in Vista too, you could set window border width to any value down to and including 0 in TweakUI. By W7, you needed to edit a Registry value to get this below 1.