I came across a reference to it when I was looking for the attribution for a quote I was using in an essay for work (that quote is: “You see things; and you say ‘Why?’ But I dream things that never were; and I say ‘Why not?’”, in case you were curious), and thought the brief plot summary sounded interesting, so I added it to my list. This despite thinking to myself "self, in all of the George Bernard Shaw books and plays that you were forced to read in school, you hated precisely all of them. Why would you possibly think that you're going to like this one?"
Unsouled, and the Cradle series as a whole, is described as something called martial arts fantasy. The magic system has defined levels of skill, with each skill level gaining distinct abilities and possessing unique attributes. It's not a design that I generally prefer, but it worked well in Unsouled. Which matters, because Unsouled is not necessarily the kind of book that you read for the compelling characters or political drama. You read it for the vivid magical fights.
Speculative fiction, broadly, includes the stories that are typically classified as science fiction and fantasy, but if you've written in the genre realm for long, you may have noticed that the terminology employed by libraries and other sources to classify genre fiction is somewhat limited. Maybe we genre writers aren't as "serious" as the "real" authors, but that hasn't stopped us from developing our own terminology to help describe our works. Since I think that many of these terms would be useful for both readers and writers to know, I've sought to describe some of them below.