Good ideas, poor execution. 'The Guns Of The South' is probably his most famous book, but I didn't think it was written very well. It read like something at a 7th grade level.
Turtledove has a couple of long-running SF series, both of which reached the "Tediously obvious he's just milking it" stage for me long before he stopped, if he ever did. One starts with the basic outcome premise from
Guns of the South (Otherwise unrelated to that stand-alone book), the other starts with an alien colonization fleet arriving to conquer us in the early days of WW2. He has a couple of other fantasy-ish series like the Atlantis one mentioned above.
He grossly overuses a couple literary devices, one of the worst is having one humble character come up with inventions or innovations that in real history arose in diverse places and involved the work of different teams of some of the best engineering and technological minds of their times, or be in so many significant events that the entire staff of all the newsreel companies in the US in their prime couldn't match his actor.
His attempts to conform historical characters to his story line and unfortunate attempts to force analogs of historical events and battles into outcomes on his alternate timelines pretty much killed my willing suspension of disbelief, particularly for the series on the North vs. South, which lost me completely along about the late Interwar period analog.
