I'm a great fan of Alt History, Guns of the South was a fun read.
Turtledove's "How Few Remain" was better in the first two books.
Basicaly The South wins the Civil War, But this leads to a second civil war a few years later which ends up in a sort of draw, of course the Euro Trash gets involved and both the North and South become entangled in the Euro allinces that lead to WWI However in Turtledove's time line WWI is not fought on the fields of Flanders, but in Kentucky.
In the books of the series after WWI Turtledove seems to run out of ideas for the main historical characters Like Teddy Roosevelt, George Armstrong Custer (Custer ends up being a sort of semi-senile Ferdinand Foch like Allied supreme commander in Turtledove's WWI in the America's). In the later books all of the really intresting historical characters dissapear and Turtledoves attempts at intresting you in new invented storyline characters fails completely...leaving you wanting to throw the book at a wall out of shear boredom and frustration.
Sorry but the first two or three books of the series were pretty good but the last couple have left me wondering why I spent good money on them.
Just my thoughts on the matter.