Like the previous game, Doom (2016), it also contains the same Easter egg that was seen in that game that was a reference to Terminator 2: Judgement Day (1991). If you fall in lava and stay in until your health depletes, you will see your hand make the thumbs up gesture, before sinking beneath.
When on the the Doom ship, if you go into the room with guitars hanging on the wall, you'll see some books on a shelf. One of them is titled, "Vault Dweller's Survival Guide", an obvious reference to the Vault Dwellers of the Fallout game series, also published by Bethesda.
The award-winning composer for the previous game, Mick Gordon, will be returning for this newest installment with another blood-pumping Metal soundtrack.
In the Slayers Fortress of Doom, when you go into the one room that is basically his office, on his desk you will see the Soul Cube from Doom 3. The Soul Cube was also last seen in the previous game, Doom (2016). It was in a room early on in the Lazarus Labs.
First Doom game without a pistol in the arsenal.