As far as post-apocalyptic invasion novels go, Black Autumn: Conquistadors is surprisingly good. Oh, it certainly has all the political baggage of the genre, and at times it’s too realistic for its own good (for instance, giving the villain a fleet of tanks to capture, then hampering them for lack of fuel), especially given how it’s ultimately still a story of Heroic Americans Fighting Back.
But it has legitimate advantages. The antagonist comes across as one of the best I’ve seen in this type of book, even if he leads from the front far too often. The action and pacing are effective. Finally, it being a postapocalyptic invasion novel instead of a “normal” one, like the Survivalist, actually makes it more “believable”, because removing the conventional opposition via apocalypse takes away the biggest objection.
The authors have the experience and writing style to make it stand above the pack. Not dramatically far above, but still better by cheap thriller standards. And a lot of the issues are with the genre as a whole, not the specific writing.