In this video I explain why looking up and down feels weird in 2.5D games like Duke Nukem 3D.
Reading materials:
Doom engine source code review: https://fabiensanglard.net/doomIphone/doomClassicRenderer.php
Build engine internals: https://fabiensanglard.net/duke3d/build_engine_internals.php
Ken Silverman's home page: http://advsys.net/ken/
Curvilinear perspective: https://en.wikipedia.org/wiki/Curvilinear_perspective
How to Draw (non affiliated):
https://www.amazon.com/How-Draw-sketching-environments-imagination/dp/1933492732