Mixed feelings here.
For those citing Spielberg and even Kubrik, both of these people are famous for taking the source material and twisting it pretty substantially. Jurassic Park seemed to despise character deaths from the source, and The Shining was remade as a mini-series because the author hated the divergence so much. That said, both of the films stand on their own. This makes the divergence something that can be overlooked.
Regarding the Lord of the Rings....it was less about following the books to the letter and more about structuring them into three movies with decent pacing. Not absolutely accurate to the books, it cut out sections which were deemed less than necessary, and resorted some of the events to create action. As such, it was not divergent from the books but definitely not faithful.
On the other hand, we got movies like Harry Potter. Fantastically book loyal, if somewhat curtailed to fit running time.
What exists in the Fallout Universe? Well, you could use the immensely dark nature of 1 and 2 to make something like The Walking Dead with some comedy. You could use the BoS games to make a story about wanderers trying to reclaim the wastes. You could also create something like 3 and 4 that retcon their own timeline, are janky as all get out, and simply conform to whatever is popular at the time with absolutely no consistency. Personally, I'm hoping for something like New Vegas, where the factions drive the story and you get the dark humor of the setting through actually developed characters trying to live in a alternative retro-future wasteland.
This said, I've watched The Loop and Upload on Amazon. If those are indicative of the quality which we'll be getting I'm betting on a CGI Mr. Handy being the wise cracking sidekick in a world where the lulls in action will be filled with nudity and drugs rather than wit. Being proven wrong would be great, but then Bethesda is licensing this out. They sued Mojang over using the word Scrolls as a title, so who knows if they'll do anything but authorize 30 minute advertisements to go buy Fallout 4 and 76.
