Arthmoor, by and large, is the single biggest impediment to quality unofficial patches being released for Skyrim.
The unofficial Skyrim patch has massive changes to the world space to suit Arthmoor's tastes, including placement of torches, NPCs, visual design elements, and more. It's not so much a bugfix patch as it is a "conform to Arthmoor's preferred vision for Skyrim" mod. This also extends to certain decisions in Dawnguard, Hearthfire, and the last DLC.
On top of this, Arthmoor also has enough pull with Nexus staff to get other unofficial patch mods pulled to prevent "confusion in the community" as to which patch mods they should use.