This game is rated ESRB: Mature 17+ for Blood and Gore, Intense Violence and Language.
This DLC is a port from Left 4 Dead, adding the campaigns The Sacrifice and No Mercy. Initially, it was to be released for the first game alone, but since players would have to own Left 4 Dead to experience the events that explain The Passing, the developers opted to release it for both games. No Mercy was brought over as well because it was the most popular campaign. Both campaigns are available in every game mode. Players will still control the original Survivors, but will find items and Special Infected from Left 4 Dead 2. Five achievements were added, as in Left 4 Dead.