Case in point: The login screen. You have to click and drag up on the lock screen, but it's dang hard to figure that out. From the lock screen, if you click the power icon, there's not actually a way to poweroff or reboot the machine.
GNOME Boxes is a really nice GUI for virtual machine management. Except they haven't provided a way to pass Ctrl-Alt-Delete to a Windows guest. The bugzilla conversation seems to have stalled with "I don't know why we didn't put that in there."