I haven't read much alternate history or historical fantasy until recently. I thought this book was very well written, with great themes like technology versus magic. Unfortunately, though, I never fell in love with any of the characters and doubt I'll remember much of this story in a few months. Marsh was too much of a stand-up guy. His falling in love with Liv felt like just another plot point, not a real relationship. The men in charge on both sides were pretty cardboard (Stephenson and the Doctor). Gretel and her brother were moderately interesting, and at times, I found myself rooting more for them than the arrogant Marsh and Will.
Wanting to know what happened next drew me forward, but the tension seemed oddly lacking. Perhaps because you always assume you know what will happen (the Nazis will surely lose). I really loved the idea of technology versus magic and the true cost of war. This is the first book I've read where the cost of war is so clear, because of the blood price the warlocks must pay to wield their dangerous magic.
The ending wraps up a good portion of the background story, but this is clearly not a standalone novel in its own right. Overall I'd give this book 3 stars for a "Liked It" rating, but I'm afraid I'm biased against the subgenre and don't think my bias should bring down the book's overall rating, since it was well written and well thought out.