Free look

Unlike Heretic, Hexen, Strife, and many modern first person shooters to date, Doom and Doom 2 only featured the ability to look horizontally, or side to side. Free look is an ability (or in Doom's case an option) to face the characters viewing aspect both horizontally and vertically to see more what is above the players head. Doom originally came with an auto-aim feature that would fire the weapon to monsters or other shootable objects that were above, below, or straight ahead on the field of view. With the use of free look, that auto-aim feature is not needed to fire at monsters or other shootable objects that are above or below the field of view because the player can aim at those object manually.