Quick-take: Mistborn is back, and it is good.
Wax is a former constable turned nobleman. He gave up police-work when an adventure turned really bad. At age 42, he decided to turn in his guns, settle down, and fix his household's finances after his uncle's passing left a mess. That is, he decided to pursue that until everything took a wrong turn. Too wrong to ignore.
Wax is a Twinborn. It is a new type of Mistborn hero. He has one Allomantic and one Feruchemical ability. If those terms are confusing / forgotten, fortunately, the book explains it all again, though not in detail. Familiarity with the original trilogy is recommended, though I don't think it is a requirement. I find Twinborns an interesting idea. A full Mistborn is extremely powerful. Good heroes need weaknesses.
As for the story itself, Brandon Sanderson is a master storyteller. I like how the main hero of this novel is a man in his middle years. It gives him depths of experience to tap in to. Normally, these fantasy books stars superpower teenage girls or boys who has no plan and just reacts, or seems to have unfathomable insights. Wax has a plan and reacts correctly because he has seen this before.
However, after praising Wax, I must criticize the young woman main character that sometimes approaches inexplicable levels of insight and skills. The explanation is hand-waved with "learned at the university" I guess that trope could not be dropped completely. Fortunately, her character is anchored by lack of experience.
Wax's sidekick, Wayne, is also a Twinborn of different powers. The two complement each other well. Wayne's skills go beyond just burning and storing metals, and the story plays well with it. I won't go in to detail because it is a source of amusement throughout the book.
Score: 5 / 5. I've already got the remaining 2 books in my queue.