As a ordinary end user, I feel
1. Windows software are usually good at product function design.
2. Mac has a better enforcement on overall UX. The visual across different software (from different vendors) are much consistent.
3. Linux desktop is unfortunately still missing above 2 points.
Some Linux distro provides really good visual, but it only applies to its built–in programs. If you'd like to switch to the external programs, the system visual might be fragmented.
I really hope in this new wave people could make some consensus on the visual of Linux desktop.