This is not really a real online game, but a new Japanese anime based on a light-novel. The story is about 1000 players who are logged into a new virtual reality MMORPG, Sword Art Online, only to find out they must complete all 100 levels of the game in order to log out in peace (force logout via pulling off the game VR helmet renders the players dead).
What’s more, dying in the game itself means the player dies in real life as well… Sounds like a hardcore version of .hack + Tower of Druaga eh? The light novel will see the main characters go on to other games after Sword Art Online is completed, but for now, the anime will focus on SAO. Episode 1 is up, so go search for the subbed version!