For me, material design evokes feelings of being in kindergarten making crafts with colored construction paper.

Material UIs are not perfectly flat; there is usually a shadow, so I can tell an element is distinct from the layer below it. The problem for me is that it often feels about as organized as the mind of a kindergartener.

Consistency of look-and-feel is important, but consistency of organization is even more important. How confusing would GUIs in the 90s have been without the File and Edit menus?