I've been thinking about the original Doom a lot lately, thanks to revealing retrospectives including Double Fine's exhaustive Devs Play, and that new Doom WAD John Romero released last month. You'll forgive me if I call the new Doom 'Doom 4' then, as it's current title is a little insulting towards a classic. The latest news about Doom 4 is that it won't feature a disappointingly short single-player campaign—according to id Software anyway. They reckon it will last you around 13 of your Earth hours, which would be a damned good length for any FPS these days.
.@Unreal389 The difficulty level plays a factor, but folks playing at the office average 13+ hours in the campaign February 11, 2016
Of course, Billy Guns, the guy who finishes every game in under an hour, is going to complete it much faster, but considering how long I take scouring every inch of every level in games, I will probably end up taking even longer. Doom 4, by the way, is looking pretty fun, and mighty violent—here's a bit of game footage courtesy of Conan O'Brien.