Nine months and two weeks ago, we said that Deus Ex: Revision would be done "in February", and boy, we were (and the mod's makers) way off. It's actually due out this very day: we'll be able to download Revision from Steam in just a few hours.
Deus Ex: Revision offers a visual and aural overhaul to one of the best games ever made, revamping the textures and soundtrack, and adding more detail the world. But it also makes tweaks to the level design, "aesthetic direction", and world-building, which are pretty bold changes to make to a classic game. Note that Revision will only 'officially' work with the Steam version of Deus Ex.
Interestingly, Square Enix and Eidos Montreal have given the free mod their blessing, going so far as to issue a press release bringing it to the world's attention. Revision's Steam link isn't live yet (it will become active in a few hours), but until then here's a shiny launch trailer showing it off.