Ok, let's try a slight change.
Virtual World:
An immersive environment that is designed to present the user's
interactions in a 1st person perspective. Doom is a virtual world, as
are MUDS and traditional text adventure games. Pac-Man and Super
Mario Bros are not, as your representation within these universes is
presented in 3rd person perspective.
This begs the question of whether a virtual world exists because of
the way the user views it, or because of the way that the world data
is laid out. Why isn't the sum of all game boards and states in Super
Mario Bros a virtual world, or Mortal Kombat for that matter, or
Tetris, even if such universes are rather limited? Every video game
ever made would be a virtual world, right back to Pong, which is an
electronic simulation of tennis.
If you had a gigantic 3d maze of Tetris blocks, and many users spent
their time viewing this world and manipulating the blocks, wouldn't
this still be a virtual world? And the world continues to exist even
if only 1 user is present....
It seems like one must build the taxonomy anew. How about starting
from the phrase "A virtual world contains puppets controlled by the
user?"
Cheers,
Brandon