I'll try the pros and cons approach this time, just for a change.
Pro:
Flint's been writing for a while now, and I believe he's getting better at it. In the past I've found his style to be heavy-handed, prone to repetition and very unsubtle handling of emotion. There's elements of this remaining here, but it seemed much reduced in frequency and degree.
A lot of historical research has clearly gone into this - it's not a period I know well, but as luck would have it I've recently done a bit of reading on it, and what little I knew from that was correctly presented in the book.
Related to that, Flint clearly doesn't just want to use his premise to set an adventure story in a differently-evolved America; he tries hard to show why those differences have arisen, advancing both political facts and personalities in support of his vision. This isn't particularly surprising, for anybody who's been reading his better known 1632 series, but it's something that I like in theory - the practice does have some drawbacks, as we'll see below.
Finally, the plot itself did keep my interest.
Con:
A minor one first: it's been a long time since the first entry in this series was published, and no allowance is made for this. Given the heavy referencing of previous events, I think the omission of a recap of those events is a disservice to readers.
The biggest issue though is related to the research and ambition of the series. There's simply too much talk, and the plot can't carry a book of this length. While I applaud the desire to produce a book that's more than a series of battle descriptions, I think the determination to delve into every single facet of 19th century American politics is misguided. At times it feels like the author is bragging, as he throws in yet another detail about some minor person or has somebody launch into a speech in support of some policy or another (how many people these days care enough about the debate over a national bank that they want to read rehashed contemporary speeches about it?).
And to finish on a nitpick, I was very unconvinced by the description of the climactic battle. It seemed to me that the way it unfolded made no sense in a military context, but was set up simply to give the reader some emotional satisfaction. No real explanation was given as to why the leaders involved would have made those choices.
Overall though, as the rating showed, I did like it - more than I do most of the 1632 books, which have in spades all the disadvantages described here, with few of the good points.