This is a story that leans quite heavily on tropes, and still manages to be very enjoyable.

There's the trope of the prettiest girl in the village that everyone in town wants to marry, but she's fiercely independent and refuses all of them, but becomes quite fond of the hero. There's the feisty grandmother. The military leader who has to deal with an underling who, despite being lower in rank, holds power over him because he reports back to the leader's superiors and answers only to them. There are probably a few more timeworn cliches in here...

But for me it all worked. Apart perhaps for Moreno, the aforementioned underling who is pretty much a one-note character, the characters are well-drawn and quite engaging. Benton takes a lot of the spotlight as you'd expect, but we also spend a lot of time with Major Branwell and his counterpart Torres. Tracy also gets a fair amount of attention, dealing with the death of someone under his command.

As to the sci-fi elements, the introduction of the aliens works well, but I was honestly disappointed when we got into "attack of the zombie hordes" bit. That's a bit done to death, and I would have preferred to stick with just the aliens. Maybe without them the climactic battle wouldn't have had to go on quite so long...

The book isn't perfect, but it did keep me entertained throughout.