Successful shooty-guns MMO Global Agenda was a success because it was designed from the ground up to appeal to people too busy with family to maintain a World of Warcraft commitment.
Reddit user sirleechalot has build a PC in a fish tank full of mineral oil, with a Big Daddy and bubbles and gravel and everything.
Michael Louisseize has made a Minecraft map. Nothing amazing there though, right? I see more Minecraft maps than I see exploding people in computerised entertainment devices. BUT WAIT.