So. The Half-Made World is not an alternate Old West per se: it's inspired by the Old West rather than trying to recreate it, and the landscape is its own rather than ours. The Old World countries are echoes you can see if you squint at them sideways, but they have their own names, their own hinted histories. This is a secondary-world fantasy with the tech levels of late 19th century America, rather than a 19th century America gone wrong.
...unless it isn't, unless it's something else completely, post-apocalyptic science fiction with oddly explained or unexplained tech not fully understood by those who possess it. I mean, it might be. The Gun and the Line: they are not much given to explanation. They are more given to orders.
The Gun and the Line are the two main opposing forces in this world, but there are others, and they are no nicer. I think the thing that stood out for me as I kept reading was that The Half-Made World does not seem to be a book that believes in people in units of greater than one. There is no functional relationship in this book, no pair of people whose bond is strong and good and worthy, no group a person could trust or even be willing to join for a dinner expedition. And if that sounds grim, well. It is a bit grim. More than a bit. Not in the supernatural bits; that part didn't bother me. In the way the humans, when they weren't being all that influenced by the supernatural bits, weren't any better to each other than when they were.
I think that The Half-Made World does some very interesting things with being inspired by the Old West instead of by most of the things secondary-world fantasy tends to take as genre-standard, but the level of human grimness it requires is not going to be for everyone. Also its ending requires a certain tolerance for Insert Sequel Here.