Today the official DOOM twitter account gave a response to a fan asking how long the single player campaign is. I personally was not sure what to expect in regards to the campaign length especially with other FPS games like The Order 1886 and Call of Duty having much shorter campaign lengths. Have to remember also that this is a PR account and the game is still in development so we will wait and see if this does turn out to be the average campaign length.
.@Unreal389 The difficulty level plays a factor, but folks playing at the office average 13+ hours in the campaign
— DOOM (@DOOM) February 11, 2016