Fallout 4 isn't quite as nice-looking as, say, The Witcher 3, but it's not meant to run on fainthearted PCs either. It is, after all, gigantic.
Iyzik's ultra-low graphics mod is meant to remedy that -- at least, slightly. The mod pushes things like shadows, how far away you can see game world details, grass, and other small details well below the game's lowest setting. The result? It's not a huge visual change from low graphics settings, but you get a frames-per-second bump of five or so. It may not sound like a ton, but for many that's the difference between playable post-apocalyptic romp and stuttering slideshow prison.
Here's a video of the mod in action and an explanation of how to install it, courtesy of ZiggyD Gaming:
And here's a longer one from TSM Channel:
If, however, that doesn't make your wheezing machine breath a sigh of relief, bad news: this is (at least, for now) about as low as Fallout 4's gonna go. Iyzik explained:
"The majority of Fallout 4's graphics settings appear to be 'hardcoded', i.e. we can't change them. For example grass cannot be fully disabled, even if every reference that should disable them is set to disable. bAllowDrawGrass=0, bAllowCreateGrass=0...etc. None of it does anything. Textures also cannot be 'skipped' like they can in Skyrim. I'm not sure if that's because mipmaps that low were just never generated for Fallout 4, or because its hardcoded to not do that."
Bummer. Still, though, this is something. How's Fallout 4 running on your PC?