Yes, in some ways it is a bit like Fallout 3, certainly in its setting. Even in their style of dress, and the enviroment, it looks like it could actually be a Fallout 3 movie.
However, clearly it is not as we can see from the advert. I think the main difference is that this movie will lack the biting social satire that Fallout 3 has. I love Fallout 3's take on American conservativism and republican idealism, this is a game made with a point to it.
I think that this movie is a bit different, and indeed has opposite ideas to Fallout 3, since it could be seen to support old conservative views about the importance of the bible. Fallout 3 satarises religion (i.e- The Church of Atom) whereas this movie looks like it may support it.
I won't write the movie off on the basis that it has a message i may disagree with, that would just be stupid. I probably won't see it however, if i am going to the cinema this month i would rather see Daybreakers.