Spoiler-free review
Having read the original fanfiction that spawned this Novel, I must say that the Plot didn't hold any surprises for me, with the exceptions of a few things I had forgotten about since reading the original years ago. As is, I had a few 'oh right, that scene happens next' moments.
Therefore I won't allow myself a verdict on how surprising the plot is or isn't and leave it to any readers who are unfamiliar with it. Suffice it to say though it still is highly entertaining and twisty enough to keep me reading it over the course of the last few days since getting an advance copy in the mail. Be it a morbid fascination at having a look into a Nazi Victory world (of sorts) that is far less over the top than Turteldove or Harris wrote it, the idea that the British Empire, however flawed, leads the free world or seeing the depths of depravity and evil National Socialism brought over the world matters not.
This book has something for everyone among AH.com's denizens, a gripping spy thriller, a hefty dose of Alternate history (which is explained in far more detail than most Nazi Victory scenarios in a lengthy and very interesting annex) and of course hordes of dead Nazis.
That Heydrich falls into the classic villain traps of monologuing and scheming up a needlessly over-elaborate death for our hero doesn't make the book loose anything, since in this case you'd have no idea what the 'bleep' is going on if he didn't.
Neither does the fact that we never find out who killed The Old Man, since by the end of the book it's rather pointless anyway.
On the other hand, the book is not without a few, if minor flaws.
One thing is that the present tense is used in the narrative. But that's probably just a matter of preference, and I still enjoyed it greatly.
Something else is that we don't really find out what happened outside Europe. Looking at you, Japan. Though it stands to hope that this is explained further in a future novel or the esteemed author tells us.
In any case 9/10. Very enjoyable, very good read, highly recommended.