I'm going to start this review with a note about a changed name. The books were originally released in the UK with a character named Shrike. For the initial US release of the books, that character was renamed to Grike. I didn't run into this during the first book because the post-movie release of Mortal Engines had renamed Grike back to his original name, Shrike, to match the movie. The version of book 2 I read hasn't been reverted, and I was legitimately dismayed that the name of the character had changed. One I looked it up online, it made sense, but it was a bit distracting.
Very early in the book, we are introduced to a character named Nimrod Pennyroyal who is described as an adventurer and autobiographer of his adventures, and the reader is also given clues that Pennyroyal is not actually an adventurer at all. By the fourth chapter, I was annoyed by the parallels of this character to Gilderoy Lockhart, the autobiographer character from the second Harry Potter book, Chamber of Secrets, and that annoyance never fully left me. The overall plots are different enough, that I was able to enjoy the twists and turns along the way, and by the 2/3 point of the book, I was invested in the ending despite the book's OTHER major flaw.
Hester, who was introduced in book 1 as a self-actualized, scrappy adventurer, was arguably the main character of that book. For this book, she is reduced to a collection of petty jealousies. It feels like the character became a shadow of her former self, and worse, this jealousy is used as a major driver of the plot.
Ultimately, the first book was sold in the US as a Young Adult adventure, but it didn't feel like it was conceived or written for a young adult audience, which was part of its magic. Sadly, this second book definitely feels like it was written with a young-adult audience in mind. Not that it was written for young adults, but written for what someone thinks YA fiction should look like.
That said, the world building is still first rate. Outside of Pennyroyal, the villains are believable and even sympathetic. It's the heroine that becomes hard to sympathize with. Like I mentioned above, I was eventually invested in the story, but I can't recommend this book. As a complete-ist, I will probably read the other two books, and maybe even write about them here, but I'm not in a hurry to run out and find the next book in the series.