Over 22,222 downloads within ten years of release! DXN - Deus Ex: Nihilum is a First Person Shooter mod set in an alternate Deus Ex continuity. It features 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).
Besides main protagonist's horrid voice acting, it feels like an official expansion to the original.
It's that good.
Oh and go and download the soundtrack. It's terrific!