So it's heeeeeeeeere.
Fallout: 76.
While the trailer didn't actually tell you much at all here's what I can piece together:
The Game is likely set in 2097. Vault 76 has been mentioned in all previous bethesda games to date as one of 17 control vaults, set to open 20 years after the bombs drop. It was mentioned in F3, Mothership Zeta and Fallout 4. This would make it the single earliest game ever set in the Fallout timeline.
It's within the Washington area, but actually a tad further out, likely around Martinsburg just outside the D.C area in West Virginia (hence the song).
There's no G.E.C.K within the vault so no setting it up and watching a small oasis grow (a la Vault 21).
Settlement building is going to be quite a big part of this game again. (It was super popular with most who bought F4) and this is very much the "setting up of the wasteland" so expect yourself finding a few highly "themed" settlements. Also expect a few mods able to just come straight over on this, namely the Creation Club ones.
Little in the way of the older factions, so hopefully more variety in your raiders and other groups who just found ways to scrape by. Maybe some factions retconned that would make a lot of sense, like the Children of Atom, could even be an origin story for them in here.
Real hideous blow-by-blow discovery of wasteland stuff like Ghouls, Supermutants etc.
Vault 76 was supposed to have 500 or so people in it, how this will "scale" in the game is unknown but I suspect you'll be one of the last groups to leave the Vault only to find a lot of stuff gone to shit, or you're the Vault Tech employee expected to see how things go after everyone has been turfed out for a few months.
Avellone is rumoured to have had major input on this game, meaning maybe this is him and Howard getting together in the mother of all prequels.
Have to remember, Todd apparently let it slip years ago that they'd already begun working on the next Fallout game as they finished up the main body of Fallout 4, so it's had at least 3 years development time and this is the core crew that has tackled it, not one of the newer satellite studios as many people had expected and speculated.