I think half the fun of alternate history writing comes from the winks and nudges that the author is able to give the informed reader about the parallels and outright differences between what got written and what really happened. Not that this is hard to achieve in a Turtledove novel; he’s the genre’s Grisham, writing alternate history for the masses, which means that he’s not really writing out of the high school history level on most occasions. There are certainly things to spot even for more informed readers, but they’re rare. (Or else, I’m insufficiently informed; that’s likely.)
As for a review of the actual book, there’s not a lot I can say. Although Return Engagement is the first of the Settling Accounts trilogy, it’s the eighth book in the same storyline. Turtledove posits that a set of military orders sent by Lee to his subordinates early in the Civil War was not lost by the messenger, and then jumps ahead first to the 1880s to examine the new fates of such historical personages as Teddy Roosevelt, George Custer, and Abraham Lincoln against the backdrop of a divided continent, while the fledgling Confederate States face their second military challenge.
Except for How Few Remain, each of the books that follows is part of a trilogy, watching the events of first the Great War, then the boom and bust 1920s and 1930s, and most recently the second World War, through the eyes and lives of fictional characters both incidental and important. It works for him, because I’m as interested in the characters’ lives and outcomes as I am in the greater outside events he is chronicling.
Unfortunately, as I said, the similar style of each of these books makes it hard to review an individual one without delving deep into spoilers, especially this far along in the series. (Hint: he’s pretty well writing the same history we have now, except the players and outcomes are wildly divergent. His theory of human nature (which I buy into) just keeps pulling them back to the same places, despite the divergences.) The quality is as high as it was in the first book of the Great War trilogy, and consistently higher in this pure venue than when he writes about fantasy settings with parallels to real world history, or about aliens who launch a worldwide attack in the early days of World War II. Turtledove is simply a better historian than fantasist, and this series lets his talent through better than anything else I’ve read by him.
One thing I can say about this book in particular: as the series goes on, I can see things coming more clearly than I could reading the early books, and as I watch these characters that I’m interested in make clearly wrong choices, the warring sympathy and revulsion leaves me very uncomfortable, I think because of how it humanizes the actors in my world’s history. For my money, that’s good writing.