The only good thing to be said about Fallout 76 is that the latest expansion features voice work from Walton Goggins (The Ghoul, on the Amazon streaming series, but he's done a lot more work and is generally a good actor). But like Elder Scrolls Online, it pretty much just exists to print money, which is why they haven't focused on single-player games since, and the one time they did (Starfield), it basically just sucked.

Fallout and Fallout 2 are not at all the same kind of game as 3, 4, and New Vegas. They're turn-based strategy games with RPG elements (dialogue and skill points). But it's mainly strategy, where you position your pieces and manage your action points (which are present in the newer ones but more of an homage to the first two). Not saying they're not worth playing, but they're a whole other genre of game. Though, if you do like those, the Wasteland games exist as well. Fallout (the first one) was inspired by Wasteland, and Wasteland 2 came out after Fallout 3 and maybe after Fallout 4, and it was due to popular demand for a resurgence of that type of game. Now there's a Wasteland 3. Something to keep in mind if you like the first two Fallouts. Which, by the way, are always being given away on GOG, it seems like. As for 3, New Vegas is basically like a "total conversion mod" for 3. It's the same engine, with updated graphics/GUI elements, and gameplay features. 3 was my first Fallout and will always be special to me, but compared with New Vegas, the writing is just weak. Otherwise it's a lot of fun.

If you ever do go back and replay 4, do it after playing Fallout 3. There's a mod for Fallout 4 called Project Valkyrie. Get it, and the mods connected to it (I think there are 3 or 4 of them? Maybe 5). Fair warning, the modder added a bunch of adult content. For example, you have the option to turn The Institute into a sex club called "The Sinstitute." You can ignore most of the adult content. And you should, because what else it adds to the experience is worth going for. For one, first and foremost, it allows you to unite all the factions of the Commonwealth. All of them. So they all have a point when they say, "okay supreme leader, now is the time to kill all our enemies" and you have to just go with it... or the game kinda stops. With these mods, you can say "no fuck that, I am the leader and I say we will have peace." And then it lets you try that. There are skill and speech checks to actually make it happen, but you can pursue peace with any faction, considering you're in charge of all of them. Oh, and the name Valkyrie... it refers to an NPC from Fallout 3 who makes a comeback in 4 (but only in this mod). This person is essential to securing peace with their faction. They also make a mod, I don't think it's compatible with the rest, but it lets you be evil from the start. I think that's them.