If the studio got anything right, it was level design more than anything. The souls borne games (except dark souls 2) have always felt large despite the playtimes being small. There are lessons that game designers on this board should take.
>interiors should have multiple exits
<more exits gets the player to feel like they’re moving through a labyrinth like in Castlevania instead of a hallway like in the original doom
>increase the dimensions of each level
<increasing the dimensions of each level’s space is a cheap way to make areas feel larger without having to add more content or areas to a level
>keep new zones visible
<the player should be consistently able to see silhouettes of levels they will be entering in or leaving from. The images produced create a sense of scale and helps the player navigate the game
>consider verticality
>nothing breaks up the monotony of navigating through a level as much as changing the dimension that someone travels in.
Thats all. Feel free to add to this list of level design tips.