I believe the best and worst thing about Linux is its hard distinction between kernel space and user space.
Without that distinction, Linux never would have become the most leveraged operating system in the world. Today, Linux has the largest range of uses for the largest number of users—most of whom have no idea they are using Linux when they search for something on Google or poke at their Android phones. Even Apple stuff wouldn’t be what it is (for example, using BSD in its computers) were it not for Linux’s success.