Nuclear showdown by James Stanfield is a gameplay mod for Duke Nukem that adds many features such as new weapons, enemies, effects to the default game as well as usermaps - it is built so you can play your favourite usermaps with, even ones that use custom art. You can also play through Duke It Out In D.C. if you have it. The TC also includes several features for mappers like more keycards, items such as the spacesuit and toolkit, and more textures to work with.