The initial Mistborn trilogy -- The Final Empire through The Hero of Ages -- was a bit of a let-down, after all I had heard about it, despite it playing around with the usual fantasy tropes. It felt like it tried too hard, and despite an interesting magic system and some fantastic world-building, the story didn't do it for me. But I had read The Rithmatist and enjoyed the hell out of it, so I didn't quit on the series. Good thing, too, since The Alloy of Law took all that world-building and gave us a lighter, more gripping, more readable story.
Shadows of Self is the next book in the second part of the Mistborn series, which is the start of a new trilogy following on the events of The Alloy of Law. So, this is the fifth book in a series which is the first in a second trilogy, following a stand-alone novel featuring the same main characters that feature in this novel. Got it? Anyway, the novel follows along the same style as The Alloy of Law, with more humor and a less epic story arc, though there are hints that something big is brewing. Plus, even though we know that this book takes place in the same universe as the initial trilogy, Sanderson makes the connections more direct and specific in this book (and yes, that ties in with the "something big").
I like the addition of the humor in this second arc in the series. The first trilogy had little touches of it here and there, but it wasn't a large part of the series; it was a serious story with serious characters (serious). Here, there's more irreverence, though not so much that it makes the story any less serious. Sanderson doesn't waste time with getting that across, either, since these are the opening lines:
Waxillium Ladrian, lawman for hire, swung off his horse and turned to face the saloon.
"Aw," the kid said, hopping down from his own horse. "You didn’t catch your spur on the stirrup and trip."
"That happened once," Waxillium said.
On the other hand, Wayne's habit of stealing things by trading worthless items for them grow a little tiresome. Occasionally, what he picks up is useful to the story, but mostly, it's a characteristic played for laughs. Over time, it became less funny.
The book's main conflict is political in nature, pitting the low-born against the nobles. It's similar in theme to The Final Empire, but it's not quite as heady. There's more to the story than that, but it begins with Wax and Wayne (and Marasi, who has become a member of the team) investigating a mass murder at a party held by the brother of the governor. The story flows from there, touching on points from the previous four novels. It's a good self-contained story, but it's also a good start to the larger story that (I expect) will be covered in the next two books.
Speaking of which, I think series that follow that structure of self-contained stories that follow a larger arc work much better than "This is one big story that we broke down over several volumes" work better. A Song of Ice and Fire is the exception to the rule, but overall I prefer stories that can work by themselves or as part of a larger work. The first trilogy in Mistborn didn't succeed as well as the last two books have.