I want to mention "Blood Prequel" mod; I've played it a year ago and found it amazing! It was unfinished at that moment, despite that it was very cool: lots of details, interactive environment (light switches, notes, other objects that you can "investigate"), detailed storyline. It was possible to travel between levels freely to complete tasks, like in the Elder Scrolls series. You can preview this mod (youtube video) but I can't find the link to download.
By the way, maybe someone know if this mod has ever been finished? And what is the state now, abandoned forever?..
I want also to ask for the similar mods (in the style of "Blood"). I know about "Caleb vs Nazis" and the other mod, I forgot the name, where you start at the countryside, then proceed to the town, possessed by demons & cultists. Maybe there are more wads that I have missed?