I started this series despite my dislike of short stories, and although it has something to offer the genre, it's certainly not a favorite.
The first three books were entertaining, as was this one. However, the author rapidly jumps from one perspective to another, resulting in a disjointed storyline. The characters are emotionally relatable, to some extent, but some are completely flat with giant holes in their motivations.
The "slow reveal" of backstory and other details are an attempt to create suspense that ultimately fails. While I'm a reluctant fan of this technique, it only works when the characters are eventually developed, and when it furthers the reader's emotional connection to the series. In this, the author falls short.
Throughout this series and especially in this installment, the development leaves much to be desired. There are entire paragraphs that make no sense and need editing for clarification.
If you're a fan of SHTF or ZA fiction, save yourself the time and skip.