I've played FA1 and skipped the rest.
I'm currently rolling through the Valentine quest after putting up a giant wall around MAH SANCTUARY.
Went to go my power armor for this next part...
Anyways, I'm torn on FA4. It had a lot of hype build it up and the reviews show unless your a fan of it, then you most likely won't enjoy it. Personally I didn't enjoy buying a glitchy game for $60. The story-line is great. The building features, which feels like they took from Minecraft/Rust is not intelligently designed when your building large projects. It needs a feature to let you tile or buildup large projects to say the least. The slow down combat effect is fun to play with. Like a modified Max Payne engine, combined with the Fall out engine.
There's plenty more, but this game will also take a lot of time to play through alllllllllll the side-quests. The main story is fairly quick from what I read. Try to buy this one from Bitcoin vendors that list it cheaper. It has fun aspects to it but it is over priced and over-hyped.
I'm hard to impress but try to judge fairly.