I liked both FO3 and FNV. Sure, they had bugs and stuff, but I still found them great fun. And I liked FO3's plot and DLCs way more than FNV's. I also have no problem with Skyrim, so at this point, I'm perfectly fine with Bethesda doing something. There's always the mods, unless Bethesda REALLY fucks up, but I doubt the gaming community would take that well and they have to consider that.
Also, it's a trailer. Games can change A LOT compared to what can be seen in a trailer. Usually, the graphics get worse and a lot of features are added/cut, but they definitely change. I said the same thing for XCOM: Wait it out before saying too much based on the trailer. For all we know, they might just be hyping people with footage they made using FO3 stuff.
Boston sounds plausible, going by the vault numbering, since 101 was near Washington and Boston is rather close to Washington.
As for voice acting; you might still have choice for a character and have a fully voiced game. Just look at how Saints Row pulled it off. It worked pretty fine for them, so it might work in Fallout. Still, I don't expect it to be voiced, just for advertisement reasons. Or that might not even be the player character, just a companion. Or just some random guy who came out of a vault.
Anyways, enough plotting, time to wait for more info. PTW.