It's always been a bit of a dream of mine to end up on the Marathon Story page in some capacity! I would like to highlight one of the entries though, since I don't recall it making the story page so far, and that's Someplace Else / Minerva: Metastasis. These are a duology of maps for Half Life 1 and 2 respectively, by now almost 10 year veteran Valve level designer Adam Foster. Someplace Else not only uses Ydnar's majestic texture set but also explicitly references Marathon. The sequel, Minerva: Metastasis's references are less explicit, but it's always been more fun that way, hasn't it? Beyond that, it makes a few small tweaks to the HL2 formula that ends up basically supercharging it, ending up as one of the FPS experiences I've ever played. Valve themselves agree, straight up hiring Adam after release.
So, if you ever thought HL2 needed a rampant AI to guide/mess with your head/irritate you with cryptic Marathon references, then you're in luck. Say Hi to Minerva: https://store.steampowered.com/app/235780/MINERVA/