If you're a fan of Borderlands aesthetics, you can bring Fallout 4's look very close to them.
Borderlands' well-liked cel shaded graphics are easy to recognise. If you like that art style and want to have something resembling it in Fallout 4, this new ini mod changes the game's graphics to make it look like this:
User Reddit_is_wrong (great name!) showed off the results on Reddit, and posted a small guide. He is using three other mods alongside the tweark, however, so the final results may be different from you.
All you need to do is download the file at the link, set '>#define CartoonPower' to 10.0 and '>#define CartoonEdgeSlope' to 1.0. Fair warning though, on-screen text may become harder to read.