There's an old debate on whether or not Doom is just a fancy ray caster game, that it's simply a beefed up version of the Wolfenstein 3D engine. True, however, this is what Doom may have looked like if it was built using only the original Wolfenstein 3D engine, in this case the Raycasting Game Maker engine has been used.
Aside from the sprite rendering and the final levels, this video shows a nearly finished version, with no shading. I also found it difficult to decide whether to go with shaded look or not. I decided to go with shaded, mainly due to the draw distance for the enemy sprites. Being quite a short draw distance, the shaded look helps to hide the magically appearing sprites in the distance.