There was a golden period of OS X roughly between 10.5 and 10.9.

Up to 10.4, windows were too textured: stripes, brushed metal.

In 10.5 till 10.9 we got to enjoy the beauty of Aqua paired with calm, tasteful gray window frames and controls that had visible depth.

From 10.10 till 10.15 was okay-ish: the flat took over, but we still had contrast and shapes.

Starting from 11, everything became rounded, low contrast and lost visual cohesiveness.

10.5 till 10.9. We didn’t know how good we had it

I'm not against the rounded look, but the thing I hate the most since the Big Sur redesign is the "unified" toolbars and title bars. The lack of button borders is easily fixed by an accessibility setting, but yeah it's not great that I have to do this, defaults should be good enough.