The game opens on 27 October 2102, twenty-five years and four days after the Great War ended human civilisation. This makes Fallout 76 the earliest-set Fallout game to date, taking place fifty-nine years before the events of even the original Fallout and 185 years before the events of Fallout 4. The inhabitants of Vault 76 are preparing to celebrate "Reclamation Day", when they can go back out into the world and help re-settle it. Of course, when the doors open they find the world still a blasted nuclear ruin, ghouls and radscorpions everywhere and the other humans engaged in a desperate battle for survival. The game is set long before groups like the Brotherhood of Steel and the New California Republic form, so it'll be interesting to see how the game fares with many of the most iconic Fallout factions missing.
Gameplay will reportedly be at least superficially similar to Fallout 3, New Vegas and Fallout 4, with a central storyline and side-missions, but brand-new for the series will be a strong coop element. The base-building from Fallout 4 will be retained, with what sounds like an emphasis now on building up Vault 76 as a bastion against the chaos of the post-apocalyptic world. This is different from other Fallout games, where you tend to leave your starting vault at the start of the game and don't see it again until the end, if ever.
The game has been heavily influenced by survival horror RPGs like DayZ and Rust, with a focus on your character scavenging for survival in a hostile world, although it sounds like you can retreat to the Vault regularly to resupply. The game has a multiplayer mode, although it's unclear if it will be a full-one multiplayer game with faction vs. faction or player vs. player combat using the Vault as a hub (like, say, Destiny), or more of a single-player game with a coop element (like, say Far Cry 5). Kotaku caution that those expecting a full-on big Fallout RPG like Fallout 4 or New Vegas may be disappointed, which backs up the relatively short development period of the game (less than three years) and the fact that the game seems to have largely been developed by BattleCry Studios, who had formerly been working on a multiplayer shooter before the game was cancelled and they were absorbed into Bethesda proper.
Bethesda itself has been overseeing development of Fallout 76 at the same time they've been working on a brand-new, big RPG, code-named Starfield, which sounds like it will be released in 2019 or 2020, with an Elder Scrolls VI and a Fallout 5 to follow.
More on Fallout 76 will be revealed at the E3 Games Conference in a fortnight, and the game will - most likely - be released for X-Box One, PC and PlayStation 4 on 27 October this year, the tenth anniversary of the release of Fallout 3.