For me, the worst issue is the low-contrast these days between the window chrome (toolbar etc) and the main window content, plus the reduction in shadiowing. This came in - when? Two or three major releases ago?

Every day, with overlapping windows, I try to select the top of a window, only to find that I have selected a window above and behind, Drives me nuts.

There is an 'increase contrast' option accessibility. but that might as well be called 'make everything deliberately butt ugly'.

I didn't really realise how bad it is until I was using my wife's old Mac, and was amazed how easy it was to manage windows.