Harry Turtledove is spitting out books at the rate of five or six a year. And they aren't short, either --- he seems to have a contractual minimum of 600 pages per novel. Anyone pumping out fiction at this pace can be expected to run hot or cold, and Turtledove is no exception.
The original World War quartet (this one is the second in a "sequel" trilogy) was fresh and consistently exciting. Unfortunately, this follow up spends too much time rehashing the plot of the original and padding the pages with endlessly repetitive prose.
Turtledove, at his best, is one heckuva skilled storyteller, but he's never an elegant writer. In this book he is just plain sloppy and long-winded. He never lets an opportunity go by to belabor the obvious: i.e., "He didn't like it. Not even a little bit he didn't." and "He thought he saw movement. But then again, maybe he didn't, too." If the plot was lively enough it might be possible to ignore this turgid, clotted prose, but since the story moves at a glacial pace, and the characters are cardboard cutouts, it gets pretty wearying.
Even though this one ends on a cliffhanger, I've let six months go by and haven't looked at volume 3. I just can't face any more sentences like "After what seemed like forever --- but really wasn't...."
I'd recommend the World War series, or the books beginning with "How Few Remain" and the "Great War" novels. But this one... well, let's put it this way: Harry needs to hire an editor. Someone who can pull out the weeds and dig the rocks out of the ground and do some verbal landscaping. A sleeker, shorter novel without endless repetition would do much better. Hey, Harry it's OK to write a 200 page book!