Fallout 3's expansion "The Pitt" takes place in Pittsburgh and its definitely not a horrible recreation of the city, but the rivers are too clean and there's not enough graffiti on some of the bridges. This alternate timeline really did something right, I guess.

Recreation of real places aside - this is more of the same from Fallout 3, love it or hate it. Personally, Fallout 3 falls in the middle of the 3 "modern" Fallout games, and the Pitt is no exception - but that also means it's not adding anything of incredible substance. If you enjoy Fallout 3, this is a nice addition.