I Really like Harry Turtledove, and yes, I have read his World At War AND Alternate WWI series. The only problem I have with his work is that, as a Professor of Byzantine history, his prose sometimes GETS Byzantine. His details sometime get in the way of his writing. At least in my own no-talent mind.

Have you read his novella "Down in the Bottomlands?" Now THAT is waaaaaaayyyy alternate history. Modern day Neanderthals and Homo Sapiens co-existing around a great big desert hole in the earth caused when the Pillars of Hercules did NOT open up and flood the Mediterranean Sea. It is outstanding.