The killer feature that I dearly miss in OS X is decent Window management.
In Windows, I can use Win+left/right keys to make a window take up precisely half of the screen. I can press Win+up_arrow to fullscreen a window.
On Linux, I can use tiling window managers like Dwm or Xmonad to fullfil all my tiling needs.
In OS X, I can full screen or have to manually deal with each and every window. It's awful.