Left Behind is the new SP DLC for The Last of Us. It is the prologue to the main game, telling the story of Ellie back in Boston (if you know the relevance to that). This is the first story DLC that Naughty Dog has done, and they have taken the care that they shown to their main games. The quality of the story so far is brilliant! I have not gotten to the real meaty combat stuff yet, but from what I know now--Humans will be mixed in with the Infected this time! So that will be interesting.