The main theme in these levels is the Elder World theme. Levels feature more decoration and a better variety of colors than in the previous episodes. As Sandy Peterson designed most of these levels there is a great number of references to H.P. Lovecraft. The overall atmosphere can said to be Lovecraftian as the levels focus primarily on large arcane structures or locales. Many of these maps have mazes deliberately designed for uneasy exploration.
It is the only episode to include the Spawn, which Sandy Petersen states is one of the main reasons his Episode was the last. Another big reason is due to the fact that his levels were, as according to Petersen, considered to be the ugliest. Petersen felt there was some truth to that. 
Furthermore, the convoluted designs and Lovecraftian design made it useful to transition to Shub-Niggurath's Pit. John Romero felt that Petersen's design was extremely abstract and different from the rest of the team, which means the player would be presented with a mindset they were not used to. 
This episode included levels that id Software did not know where else to place, typically more difficult ones. Episode 4 is considerably harder than the other three, with even the early levels containing the toughest types of monsters. Furthermore, powerful weapons take longer to acquire than in other levels. 
The introductory text displayed in the corridor leading to this episode in Introduction reads: "Your worst nightmares come true..." The goal is to search for the Rune of Elder Magic to fight against Shub-Niggurath.
- the Sewage System
- The Tower of Despair
- The Elder God Shrine
- the Palace of Hate
- Hell's Atrium
- the Nameless City (secret level)
- The Pain Maze
- Azure Agony
|Rotfish||7 (14)||23 (46)||24 (48)||The vanilla engine counts each Rotfish as 2 enemies.|
|Fiend||35 (36)||63||92||On Easy skill level a Fiend doesn't spawn on E4M3: The Elder God Shrine.|
|Total||290 (298)||457 (480)||625 (649)|