Quick-take: A confusing end to a tired series.
And thus, the series is finished... mostly. Brandon Sanderson left himself an opening for a new adventure, which I will ignore. This series has definitely run its course.
Wax and crew head off to a new town to find his long-lost sister and The Bands of Mourning. Mostly his sister is Wax's main goal. Marisa has her own quest to find a special artifact. These motivations is laid out in an early scene in the book. Steris comes along too... because... why not? It's more comedic to have her. She does prove to be of some use.
My main complaint of this book is it seemed to dive in to cheap blue-collar comedy. That's fine when done sparingly. However, I thought a couple of the diversions were unbelievable and hurt the story.
Also, the story tossed a wrench in to a magical system that has been laid out in the previous 5 novels. The justification is that science is unlocking secrets. However, the scientific explanations made little sense, and the discoveries of how how to use the special artifacts were unbelievable.
New characters were introduced too that were bizarre. Overall, this book felt like a TV series that has ran for 2 seasons too long. Its glory days are gone and is coasting on inertia. Ratings are down, and an executive said, "Let's mix things up for some excitement!"
However, this book was still enjoyable. There was a lot to like with the final fight scene, despite it dragging a bit long.
My score for this book is a strong 3. For me, Mistborn ends with this book. Ideally, the best place to have ended Mistborn was after book 3. The Wax and Wayne series should be relabeled as fan fiction.