Fallout modder Hein84 makes some of Fallout 4's most popular texture mods, including Vivid Landscapes, which made it onto Chris's list of best mods for the game (going over that list just makes me want to reinstall). He has just released a compilation of all his work, bringing improvements in trees, landscapes, buildings, roads, and bridges into one place, and if you want to make Bethesda's RPG prettier then it's well worth a look. Best of all, you can scale it up and down based on the power of your rig.
Vivid Fallout—All in One replaces lots of the default visuals with more realistic, weathered textures (Hein84 claims they are actually less demanding on your graphics card than the originals) and sharpens some of the vanilla textures to make them look better. The overall result is a marked improvement. Take a look at the before and after shot below to see for yourself.
You can download 1K, 2K or 4K versions of Vivid Fallout—All in One to match the power of your PC. If you're not sure, you might want to opt for the 'Best Choice' version instead, which balances texture quality with steady performance, or the 'Best Performance' version if your PC struggles with that.
You can find all of the files on the mod's Nexus page. Make sure you uninstall any of Hein84's existing mods before you try this one out, otherwise it won't work.