First the writing; it's a strange blend of alternative post-war historical text, with 1st person insight. That can be a little weird when reading, but for me, writing style is the least important feature of a book like this.
Secondly, big gripe, finish the bloody war As I reached halfway I was wondering if the last quarter of the book would cram in the rest of the war. Gradually realized that a follow-up must be in the wings. Misleading to say the least as the book's subtitle is "an alternative war"
I really wanted to like this book, and I really wanted it to be more well thought out than the typical what-if. Unfortunately, it hit the same trap most what-ifs in this forum bump into; allies sit around without adjusting to the changed war, and inconvenient facts which might unbalance the what-if are left out.
For example, as you can guess, the main POD is that the Germans make Moscow a priority in 1941 and take it. They take it without a fight, no Stalingrad 1941, no heroic defense, they just march, cut off the capital which has been conveniently abandoned by the red army.
Furthermore, those troops in Ukraine who were IRL subject to an encirclement and capture, simply sit in their trenches, pesumably drinking vodka while the Germans go north. No counter-attack, no probing German weakness, they are not even mentioned until conviniently captured after the fall of Moscow.
At this point the author does attempt to introduce some German mistakes; a failed encirclement at Gorky, Hitler's interference after his recovery from the accident which prevented his decision re Moscow earlier, but it is not enough to redress the balance. Russia fights the war according to the original script while the Germans correct all of their 1941 mistakes and transfer chunks of armour around the place without other fronts being affected.
The second major divergence is Africa. Although not really advertised in the book, North Africa plays a major part. Again, Germany correct mistakes, and worse, have no supply problems.
It is decided to double the size of the Africa Korps in 1941. This has little affect on Cunningham's Crusader plan which fails on schedule. However, at this point a German/Italian invasion of Malta takes place, within range of alled air cover and with paratroopers Hitler ordered never to be used. No attempt was made to reverse Hitler's post-Crete decision, they just go and take Malta.
Shortly after Malta, Rommel launches his historic march to El Alamein, but heavily reinforced, with no additional supply issues, and with the garrison of Tobruk sitting and waiting to inevitably surrender. As well as the uncontested fall of Malta, the lack of an attempt to evacuate Tobruk which would have been made in these circumstances, conveniently allows the city and port to fall to Rommel.
Then it's a quick jaunt up the Via Apia, only without allied air harrying supply, and without new trucks to carry the extra fuel (which I presume had to magic it's way into AK petrol tanks) Rommel unsurprisingly takes all Egypt. Wherever an attempted British defense might have made this impossible they either conveniently flop - around Knightsbridge, or withdraw - east bank of Suez.
I think the author makes both deviations from history believable; but only from the German side. With a little more thought, the author may have been able to break down the potential obstacles to the alternative history, but by sweeping them aside, ignoring them, and keeping the allies fighting a different war, the what-ifs fail to be believable for me.
Aside from that it's a good read, and for the most part, the book reads like a detailed history of the two fronts, down to a corps and sometimes divisional level. There is great detail there, and with a large dose of suspension of belief, the alternative campaigns can work.
To summarize, my real beef with the book is that suspension of belief should be taken care of by the author. I should not have to pretend to ignore the pitfalls in order for the alternatives to work.