Global warming made the sea level rise. Boston actually looked something like this in the 1600 too, before Boston (which was itself an island) was filled in, there were more, larger hills to the west and they took from them and filled in these areas, also flattening the western parts. I'm from Boston too. Still, to this day the boston metropolitan area sits on water. If you go to the Copley library, there's an access door, that if you open you can see nothing but deep water. If i...
Even Fallout 3 was not small. And remember how difficult it was to get to some parts of the city? Boston has a subway system too, so there will be a lot of that. And I'm sure those bridges on the map have stuff on them making things difficult. Maybe the water is iradiated and hard to cross. There's no way to tell without playing, but I wouldn't expect anything to be less. Fallout 3 was about 4 or 5 Gb if I remember right, and this is around 30. I wouldn't worry about th...