My main impression of Windows is that all the 'old' NT kernel stuff is very solid and still holds up well, that there's a 'middle layer' (Direct3D, DXGI, window system compositing) where there's still solid progress in new Windows versions (although most of those 'good parts' are probably ported over from the Xbox), while most of the top-level user-facing code (UI frameworks, Explorer, etc..) is deterioating at a dramatic pace, which makes all the actual progress that still happens under the hood kinda pointless unfortunately.