Deus Ex: Nihilum (DXN, DEN or Nihilum for short) is a First Person Shooter mod taking place in an alternate Deus Ex continuity - released on May 28th 2013. It features new made-from-scratch original content, while also extensively featuring material from the UNATCO Born mod (used with permission from fender2k1, UB's project leader) and Deus Ex: Revision (2011 build - used in accordance with the mod's license).
Deus Ex Nihilum is probably the best singleplayer mod for Deus Ex. The atmosphere in this mod is fantastic! It almost feels like you are Agent Ingram. Musics.. holy crap! Absolutely amazing! The musics are so good that I even listen to them from car stereo while I drive to work. Level design is fantastic, although some levels are really confusing. It might get a little frustrating when you don't know where you're supposed to go and there are like dozens of doors that are locked. I don't mind it though.
Overall Nihilum is an amazing mod and it's definitely my #1 favorite singleplayer mod for Deus Ex.
What are you waiting for? Go play it now! :)