While most of the levels exist highly ruined, the developers first built every level as if nobody had ever walked in them. Going through each level with special developer-only 'weapons', level designers would then dismantle the levels in order to create a highly damaged effect.
The game contains several references to the original Doom games. For example, one of the magazines lying about has a "surprised" face on it - that of the Doom Marine from the first two Doom games. Also, the "player face" on the arcade machine is that of the Doom Marine.
The PDA audio logs closely resemble the format, tone, and pacing of the audiotape Ash listens to in Evil Dead 2 (1987).
Originally was not intended to be made. John Carmack, unimpressed with the current plan for the company's next game, told his co-owners that unless Doom 3 was id software's next project, he would quit.
In the original Doom, the player lost all their equipment (except for a pistol and 50 bullets) at the beginning of every new episode (for a total of two times). Although no reason was given for this effective "restart" in every chapter, the concept was carried over into Doom 3, and the player loses all their equipment (twice), on the journey to and from Hell. There are also several other holdovers from the original doom, such as a boss fight that consisted of two Barons of Hell, toxic sludge, and more.