It took a while, but I just finished it now. In the end, I have mixed feelings. I'll try to discuss it with a minimum of spoilers, but feel free to skip if you don't want anything revealed.
The book is very well-written, I'll give it that. Turtledove can always be a snappy writer with good turns of phrase. And like I said before, his choice of POV characters struck a good balance between providing the everyman view of the story's events and the leaders' view at the head of such events. Turtledove struggled with this in the past; in TL-191 for example, How Few Remain focused entirely on the point of view of leaders/historical figures, which left me wondering what the common man was experiencing. But in the Great War book trilogy, he swung to the opposite extreme and made all the POV characters everyman characters, which left me wondering what Theodore Roosevelt, Woodrow Wilson, and the rest were up to. This style strikes a good balance by showing how Joe Steele's regime changed American life, while also showing enough glimpses into Steele's inner circle to see how things operated at the top.
The story truly does run with its basic premise: U.S. President Joseph Stalin. I think people can argue back and forth all day with no resolution about the plausibility of the events that follow. America sees gulags, collective farms, and government/military purges. Would that actually happen in real life? I don't know. It was the Great Depression and World War II, and maybe, as the book argues, people would go along with it, since desperate times call for desperate measures and such. Maybe the Constitution would've been strong enough to place Steele on a leash. It's pointless to argue, so I'm sidestepping that question.
Perhaps my biggest disappointment with the story is that Turtledove didn't take more advantage of the moving parts that this world created. Again, TL-191 fell into this same trap; that saga wound up bring us two major alternate history scenarios for the price of one: a Confederate victory in the ACW to start, followed up by a Central Powers victory in WWI. One of my biggest gripes about TL-191 is how Turtledove did next to nothing to take advantage of the latter; a CP victory would be a huge paradigm shift that would have major implications on the cultural course of Europe and the world. But next to nothing is explored about the huge changes this could bring about, and the SGW in Europe ends up being little more than World War I with 1940s tech.
Turtledove had a similar disappointment with "Joe Steele." The basic WI premise, U.S. President Joseph Stalin, is supplemented by yet another, oft-speculated change with a lot of potential: Leon Trotsky's Soviet Union. Think of the huge changes this could've brought in the 1920s and 30s! Trotsky could've actively promoted Permanent Revolution throughout Europe, leading to even more intense Red Scares throughout the continent that change their political dynamics! Soviet Russia could've developed a much different economic and political structure, depending on Trotsky's decisions. Hitler would've had a field day rallying Nazi Germany against Russia, now that they were led by the man who they could demonize as the personification of Judeo-Bolshevism, leading tensions between the two to rise to being white hot, and further changing how WWII ends up happening. So many possibilities!
And what does Turtledove do with these possibilities? Nothing. Nada. Trotsky is just OTL Stalin with a different name. Just as oppressive with just as many prison camps. Same foreign policy decisions. When Trotsky ends up signing what is essentially Molotov-Ribbentrop with Hitler, I literally groaned out loud. You've gotta be kidding me! And then World War II in Europe goes off identical to OTL, with the same resolutions between the Western powers and USSR, without a hitch. An absolute crushing disappointment. No interesting butterflies, no nothing. At least Asia got shaken up and changed pretty significantly.
On a more micro level, a similar problem emerged with the changes in U.S. military leadership that ensued. Joe Steele purging the military of officers who failed in battle had the potential to change the course. It resulted in Omar Bradley being in charge in Europe, and Eisenhower leading the way in the Pacific. Again, this introduces another potential moving part, as the two officers could've made different military decisions than those employed in OTL. But once again, things take an identical course to OTL, which is a letdown.
It's especially glaring because Turtledove actually paid good attention to a pretty good butterfly closer to home: because Joe Steele is paranoid, authoritarian, and purges people, there's the significant butterfly of no atomic bomb during WWII. Besides providing yet more intriguing, oft-speculated ATL developments (Operation Olympic implemented, followed by Japan divided between a communist North and capitalist South), it's a good attention to detail that shows one of the most likely changes that would've come about because of how Steele was running things. I just wish Turtledove had taken more risks like these when he had the opportunity elsewhere in the story.
Incidentally...poor Japan. It was hard to read just how much that country suffered in this story.
In the end, the story itself was decently written, an engaging page-turner, and as mentioned before, the ending was pretty chilling. I think thematically, the story did a good job of describing the cultural contradictions of this darker, more authoritarian United States, the dilemmas citizens feel as their country becomes stronger, wealthier, and more prosperous, but less free, and how, exactly, they should feel about President Steele's place in history. Just like how TL-191 transplanted Hitler's Germany onto America, we've now seen Stalin's Russia played out in the USA. And while the former did a decent job exploring the scars brought about by destruction, defeat, and genocidal horror and guilt, the latter does a good job of exploring the confusion, uncertainty, double-think, and fear brought about by living under a brutal, yet effective and victorious tyrant. And unlike Khrushchev taking over the USSR, things aren't about to get any better for post-Joe Steele America.
In summary, well-written story with good perspective, interesting themes, and some intriguing changes when it makes the effort, but could've been better if it made full use of what it had to work with. 4 stars out of 5, imo.