I would say that MyHouse.Wad is the thing that inspired me to remember why I loved horror in the first place. It truly is a unique experience and I really love the inspiration with it. Totally convinced me to read the book it is heavily inspired by but really showed me that more people CAN do the Silent Hill thing of a strange place with strange logic and still draw people in.
The music, gameplay, ambience and aesthetics all mesh well and really give me a SH2/3 vibe while still feeling fresh.
Golden Souls is also a great mod and I'm so glad the Doom Mod community exists to bring all these creative ideas that people have to fruition.
Sidenote: It also inspired me to write a weird west setting for tabletops that I hope to release at some point.