At least as far as the UI is concerned:

- No focus-follows-mouse options means I can't layer windows in a way that accelerates my workflows. Having to switch between windows constantly is a giant speed bottleneck for me.

- No keybinds for quickly resizing and positioning windows as far as I know. I only use the mouse to quickly position windows and even then just use alt-drag on my Linux desktop.

- Animations. Anything that doesn't just instantly do whatever I told it is wasting my time. I don't need pretty or shiny.

Of course this is my own personal experience, but I am extremely less productive on Mac and Windows compared to Linux due to these and more.