Like how Doom 64 was darker, creepier, slower, and more atmospheric than the classic Doom games? Then use the D64ifier to D64ify your game. Make Doom, Doom II, Final Doom, No Rest for the Living, and most other vanilla mapsets look, sound, and feel like Doom 64.
Another example of the types of improvements being made for the next release of the D64ifier Hi-Res Texture Pack. This shows the drastic difference in the normal map for the glowing red rock textures.