Looks like XFCE redid their icons based on our most recent GNOME icon style :P
A bit of pedantry:
- Ideally all icons should cover a similar area, but since all base shapes have the same height here, the square icons are way too big
- A number of icons that really need some gradients/3D don't have any (e.g. the coffee cup in the preview icon)
- Some icons have Tango-ish 1px lines and gloss, which feel out of place (e.g. the x and gear emblems in the top left)
@m4u9 Happy to! Join us on gnome-design on Matrix/IRC maybe?
My main suggestions would be to stick to the more balanced base shapes we use upstream, and use shading more consistently across icons.
For example, the battery and displays are shaded like 3D objects, but the simple square icons don't have any shading at all. Upstream we use the shiny "chin" on icons like that to keep them grounded in the physical metaphor (but also, we try to have unique shapes wherever possible).