KDE’s Visual Design Group recently put some thought into shadows in Breeze. Right now, the default shadows are rather small, and can be almost entirely invisible on the left edge:
We decided to make them larger and deeper by default, and center them horizontally so that there’s a shadow on the left edges of windows and menus as well. I was honored to produce the patch, and I’m happy to report that it’s been accepted and merged! Starting in Plasma 5.12, here’s how shadows will look:
These are just default settings of course; if you don’t like big shadows, you can tweak to your heart’s content (System Settings > Application Style > Window Decorations > [click on the little menu button in the corner of the Breeze entry] > Shadows). But this new default setting provides a much greater sense of depth that I think most users will find quite welcome.