The game has a story with NPC's, and much more robust crafting mechanics and an entirely player-driven economy as opposed to looter-shooter bullshit. Like, pre-NGE SWG, Ultima Online, EVE Online levels of player-driven; players have to specialize, and they can't even do much more than stabilize themselves back up to 20% health, or even clear rads, without a Medicine-specialized PC or NPC around. Only the most basic of sustenance and scavenged food isn't crafted, let alone decent weapons or armor. To get anywhere or do anything, players have to work together, period, the end.
So, the story. About 9-12 hours long, designed as a protracted tutorial and to introduce the game world. Players emerge from the Vault, with an initial mandate to gather and start building at a nearby, randomized, pre-selected location, with your typical "how to gather, build, eat and drink, find weapons, etc." introductory quests that take 30-45 minutes to complete. The culmination of the intro quest is a trip into a nearby ruin, to repair, activate, and attenuate a repeater station, which enables global voice chat for that character and allows them to listen to the radio stations, etc.
You do that, and...oh, wait. There's a radio station active that's not coming from the Vault or other players! Somebody survived the holocaust...better check that out. But, it's up to the player to triangulate the location of the signal, based on signal strength. Eventually the player makes their way down to the mines, where they find a ghoul settlement. The player learns more of what's happened since the bombs fell, who ghouls are and what they're doing (they're survivors from the war, gathered for safety, and are trying to make a home for themselves), help out maybe, and eventually learn there are two major groups of raiders in the area in addition to the little pockets of raider-ness around.
One group is a pretty straightforward coalition of raider gangs, and they're a full fledged faction too with whom you can trade, do missions, etc. Typical raider stuff, go forth and be an asshole. Drugs, slaves, rock and roll, automatic weapons, all the good things in life.
The other group...well, the ghouls were "misinformed". It turns out this is a pretty sad group, they're refugees who moved into the region because it's one of the only places around that can support life. They lack resources, the older members of the group are dying off to various radiation-related diseases, and the post-war kids and young adults were never formally educated, but have learned the hard way how to survive in the wasteland. In other words, they're proto-tribals; they haven't completely regressed to pre-modernism, but without help, in a generation or two that's where they'll be.
That introduces three factions to the wasteland. Everybody hates the raiders, and the raiders want to kill, assimilate, or enslave everyone else. The tribals think the ghouls are all feral, and want a safe place to live. The ghouls think the tribals are assholes who want all the scant resources of the region for themselves. That's the game setting initially, and it's up to the player to decide for themselves with whom to side, and how they think conflicts should be settled.
Except the monkey wrench in the gears is, you're in a server with a bunch of other people, they may not agree with you, and quests from one faction can and will come into conflict with quests from other factions. Including "live" events and dynamic quests. Except, these quests and events don't necessarily involve PvP: players can negotiate and compromise, and return to their respective quest-givers and select dialogue options that reflect peaceful resolutions...that is, if they aren't screwed over, at which point PvP on.
So, let's say for instance, a live event pops where the Nuka-Cola plant gets overrun with mirelurks. Go figure. The ghouls decide they want the Nuka-Cola plant for themselves, figuring if they can get it running again they can score caps out of it trading fresh Nuka-Cola to caravans. The raiders, on the other hand, aren't interested in the Nuka-Cola itself but rather turning the place into a monster drug factory and shooting gallery. Players converge on the Nuka-Cola plant.
At this point they could clear out the mirelurks and have a nice big shoot-out to seize the plant for one faction or the other, and return for their payout. Or...they could negotiate and mutually decide on a peaceful resolution. Say for example, the ghouls get the plant but make drugs on the side for the raiders, who provide "security" in exchange for having to do none of the real work.
Now, this option has a nice payout and earns reputation for both factions, but not as much as seizing the plant for one faction. Which is important, since at this juncture the PC's can select a "double cross" dialogue option, and based on the number of "double cross" choices taken and the CHA/speech rating of the PC's, the faction can do that instead. If one or both factions decide to double cross, the shootout commences nevertheless.
Anyhow, this portion of the story continues, and the player reports back to the Vault 76 Overseer, who stayed behind to communicate and coordinate with other departed Vault-Dwellers, and eventually gets told to check out power fluctuations at the Greenbrier hotel. They go there, find the Greenbrier bunker, and when they enter the PC's Pip-Boy lights up like a goddamn Christmas tree. The facility opens up and comes to life, robots start coming out of hibernation, patriotic music starts playing and the stars and stripes are everywhere, and the player is...welcomed?
Because Vault 76 wasn't a control vault. It was an Enclave vault. Its purpose was to open twenty-five years after the bombs fell, and its dwellers were intended to be scouts to assess the habitability of the wasteland. You were working for the Enclave, gathering intel on the waste and its inhabitants, the whole time.
The Greenbrier was one of the Enclave's CoG bunkers, but it lost contact with the outside when the bombs fell. Without outside contact and orders, the Enclave fell back on a contingency plan of entering cryogenic stasis to await an all-clear from Vault 76. The Overseer's original intent was to send a dweller immediately after establishing a base camp (the tutorial), but upon learning there were other survivors decided to wait and gather information. Now that the Overseer has the information they need, they sent a dweller (you) to the Greenbrier to physically deliver the all-clear since radio contact was impossible.
The Enclave stationed at the Greenbrier come out of cryo, welcome you, review the Overseer's intelligence and brief you on their plan. The Enclave needs the region's coal as a fuel supply, and the Greenbrier's mandate was to seize it. Except, those pesky ghouls, raiders, and tribals need to be dealt with; the tribals can be exploited as a manual labor source, the raiders need to be eliminated, and the ghouls are filthy disgusting mutants to be eradicated. You're trained in how to use power armor and craft energy weapons by the Enclave, receive a fast travel option in the form of Vertibird pick-ups and drop-offs, and sent forth to conquer the wastes.
Oh, and here are the locations of a couple ICBM silos you can use to dispatch the raiders. Of course, whether the PC uses them that way is up to them; they could nuke the coal mines, which actually wouldn't hurt the ghouls but render them uninhabitable to anything not a ghoul, or turn the nukes on the Greenbrier. Maybe disable them so they can't be launched. Or just nuke random-ass landmarks for funsies. Either way the post-game is here, and the main body of it is dynamic quests and events to support your faction(s) of choice with, or against, other players at their leisure.
