It was the first such game
to serve up proper 3D, or at least
to do so in a smooth, playable way; it standardised the FPS weapon set of pistol, shotgun, machine gun, energy, rocket launcher and totally - insane - last - resort weapon; it made blood and gore
key parts of the FPS experience; it birthed the idea of varied baddies who needed
to be taken down in different ways and possibly with different weapons; it
basically set the tone for
everything that followed for years after.