It was okay but I found nothing to love in the book beyond some fluid writing here and there. The story felt like a grab for a movie deal. (Teens! A boy! A girl! A villain! Hotness!) 
 I just didn't like anyone in the story. 
 The ridiculously nasty villains were actually the high point. (I shall walk on the bones of my enemy!) The protagonist with manufactured angst ("who am I? why am I a captive if I am so powerful?") couldn't inspire me to root for him. The duoprotagonist/non-romantic secondary lead had no moral grounding ("I'm gonna be a pirate and victimize people and have no empathy for anyone I have stolen from even though I've strangely bonded with an innkeeper who would otherwise have no place in my life but who mysteriously takes me in when I need a place to hide from the law"). The royal "brother" had an inner life as deep as a piece of tissue paper. Kell's role and duties and privileges in that society were ridiculous. The technology of Redworld made no sense (with flashing electronic billboards but 1800's society and naval capacities). 
 The three worlds weren't inspiring ("look a glowy river and a strange monetary system and a mean mean tyranny where no one seems to have any basis for an economy"). 
 I wanted to like the book. I didn't like the book. 
 George III died around 1820. Revolvers weren't invented until later in that decade. I googled it.