Yes, I have a copy of Guns of the South. It's his best novel, I think, and certainly his most well known. Besides being an interesting sci-fi concept, it approaches the question of the civil war and slavery from a different angle by contrasting the period characters with the modern racist extremist. My only gripe with Turtledove is a lot of his dialog ends up sounding the same. I've tried some of his other alternative stuff, like the Great War and American Front, but they read too much like Guns of the South and Worldwar. I think maybe he's cranking too much stuff out at the moment. Some of his earlier short stories have excellent mood and dialog. I stumbled across a short story he wrote in 1988 called "Gentlemen of the Shade" about vampires, and didn't even recognize it as being his writing. The dialog in the Worldwar series suffers a little bit from this, but I think it can be forgiven because overall it's a ambitious story with scope dealing with race, international politics, the impersonal brutality of mechanized war, and the personal brutality of the Maoists, Soviets, Nipponese and Nazis. It is a pretty depressing, I'll admit. There's little hope for a victory for the human race, only a stalemate. There's another three books called Colonization which advance the story into the 1960s when the colonization fleet is due to arrive. It's a little bit of an unsatisfying sequel, because there are tantalizing hints that the human race might be able to rid themselves of the Lizards, or at least corrupting them to the point that a distinction would be a moot. There's also the hint of attempting contact with the Lizard homeworld. However, none of these plotlines are developed and are so far off anyway as to be not within the scope of the existing novels. Supposedly, Turtledove has released a fouth and final book in the Colonization series this fall which I haven't read yet.
The one weak point in the Worldwar series I though was the Lizard's supply of nuclear missles. Truly, if they wanted to, they could push an asteroid ala Footfall to compensate for their dwindling supply of nukes. This capability is hinted at as a human tactic in the second series.
The End Of The World Part Two.