I've lived through every evolution of Windows from 3.1 up to 11 and Millenium/2000 still remains my favourite and I will always consider it the most 'get-shit-done' UI that Microsoft has ever built. Up until W10 removed the feature, I used to turn off the Themes service so that I could get the classic UI back.
And I also completely agree with your point that everything else since then has felt like a poorly placed theme on top of something else.
And I also completely agree with your point that everything else since then has felt like a poorly placed theme on top of something else.