Deus Ex Unreal Revolution is a mod for the original Deus Ex that acts as a parody of Deus Ex: Human Revolution while providing commentary on the video game industry and modern gameplay mechanics. Features yellow highlighting, cinematic takedowns, iron sights, and regenerating health.
It came, it saw, it conquered.
It was released out of the blue (and apparently made in a few weeks), it looks great, the gameplay mechanics are well implemented and it's packed with great referential humour.
While not a full-fledged mod per se, it's definitely worth everyone's time. :]