Excellent visual comparison between macOS Catalina and Big Sur (see link below). Here are a few observations:

  • Big Sur design is a step back in clrity in many areas. Ex.: Icons and segmented controls in top portion of windows.
  • More padding around items lists. I’m not sure why. I prefer Catalina’s version.
  • Dark Mode is slightly better looking in Big Sur.
  • Battery panel in Settings is horrible.
  • Gone are popup alerts at the top of windows, they now look to be centered within window content and movable. Catalina is better.
  • Menu bar is translucide. Catalina is better too.
  • Safari is much better looking in Big Sur.
  • Notes is much improved in Big Sur.
  • Big Sur icons shapre are much more uniform. Advantage to Big Sur here.
  • Big Sur Side Bars in many apps like Maps is better looking too.

Who wins? Well, the jury is still out.