Indeed, Wolfenstein 3D revolutionized the industry but had no multiplayer. The fun thing is how these games actually made it into the former Eastern European bloc. In the early 1990s virtually nobody had home computers, but I went in weekend to my father's factory computing lab (he worked as tool design, later quality assurance engineer in a factory producing screws and various other small metallic parts) and played Wolfenstein 3D. Back then, they were still using a computer with punch cards, but we obviously didn't play Wolfenstein 3D on that one... :)