I've read 1* reviews of this book and I've read 5* reviews, and I can see where both of them are coming from, though I definitely lean in the direction of the latter rating. 
 This is a long review so here is the TL:DR for the impatient among you: 
 This is a very well written book - by which I mean that the writing is excellent. Ironically that writing may well be a barrier between many readers and enjoying it. 
 This is an interesting book - by which I mean it evokes interesting questions of a literary nature. It is not a book with a well-engineered plot where everything comes together in the end with an almighty bang a la Sanderson. 
 This is a grim book - Nasty stuff happens to innocent people. The level of detail is often small in these instances but the quality of the writing makes you cringe at them even so. 
 This is a book I advise you try - I don't know if you will like it but it's a bold experiment and feels like something new. 
 To the review! 
 The most popular 1* review of this book says: 
 The writing in this book is killing me already. For example: "Big as a cart horse. Deep fetid marsh rot snot shit filth green." & "Imagine saying that to Gulius's family: he was killed fighting a dragon. He was killed fighting a dragon. A dragon killed him. A dragon." 
 I understand the reaction but disagree with the implication that the writing is not good. I think the writing is excellent, but it is certainly not the sort of writing that fantasy fans are used to. This is a book written in a refreshingly literary style more familiar to the readers of literary fiction. There is a strong voice to the prose, which I liked a lot. I needed my word-brain exercised after the last couple of books I dipped into and abandoned where the words fell dead on the page. 
 However, many fantasy readers will not like the change. This is in no way to suggest that they lack the intelligence or sophistication to appreciate the work ... just that it will not be what they were expecting. 
 As a case in point, consider one of the offending lines from above. "He was killed fighting a dragon. He was killed fighting a dragon. A dragon killed him. A dragon." Writers are schooled against repetition and redundancy. But everyday conversation is full of these things, especially when we are wrestling with a concept. Dialogue in fantasy books is generally a stand-in for genuine conversation. Playwrights do not write dialogue like fantasy writers do since they need the audience seeing the person speaking the lines to believe in them, there and then, in the moment. Some of the dialogue in TCoBK follows this style. 
 The book moves from first person to third, from present tense to past tense, takes an omniscient point of view at times, and varies these things for a given character. The effect can be quite dramatic and powerful, but also may unsettle a reader. 
 Fantasy writing is generally all about the story, specifically: all about the plot. Many readers want prose that draws no attention to itself whatsoever. A line that makes a reader sit up and notice is, by some lights, taking the reader out of the story. The prose, some say, is a plot delivery mechanism. This can work very well. I really enjoyed the Brandon Sanderson book I read. The writing delivered plot and I didn't notice it. You will notice the writing in this book. 
 "The moon was vast in the sky, the stars broken silver." 
 I've not found eminently quotable lines so much as a constant stream of elegant, poetic lines that do their job. The linguistic skill is aimed mostly at description rather than at aphorisms. The effect is cumulative over a page rather than shining from one line. 
 Speaking of plot: this is a chaotic book where it is very hard to predict what will happen next and where. I never had a sense of overarching plot. It is more a series of things that happened, though focusing down on two characters and their journey toward an uncertain destiny. This is not a bad thing, unless you really need a plot. 
 The next thing that fantasy readers tend to like are characters. If they aren't all about plot then readers tend to be all about character. I've had my own struggle to convince readers to get on board with books about characters who are merely interesting rather than good/heroic/moral. I do though, I hope, throw the readers a bone by making them charismatic and/or funny to compensate in some way their despicable elements. 
 TCoBK goes a step further and presents us with characters who are generally horrible in almost every aspect and lack even humour or charisma to hang onto. The main character in particular is very hard to like and whilst there are interesting things about him I never felt emotionally engaged with his plight, or indeed that of any character in the book. 
 The pacing has been mentioned, and it can be erratic. Toward the end there are several longish contemplations of the countryside, and the description there is just excellent, really beautiful. But pacing-wise ... not so sure it was the best place for it. Description throughout the book is a strength though. 
 Grimness. This book is pretty grim, not so much for the gory detail but for the things that are done, the way they are done, and who does them. Babies are killed, children drowned, young women mutilated, innocents burned, murder abounds, kindness is in short supply. 
 Despite the level and quality of description I would say the book is physically shallow and thematically deep. The cities and wilds are described wonderfully but with the characters it never feels as if we are physically deep in them. Several of them get burned, beyond a mention of it aching the issue is pushed aside. Injuries and mind-wrecking hangovers get similar short thrift. Being exposed to a cold wind for the first time, snow, having sex for the first time, all similarly relegated to the background in favour of more existential angst (not said in a mocking way - I like existential angst and suffer from it myself). 
 However, it is still, to me, an interesting book. It feels as though there are themes being addressed here. I'm not going to (or qualified to) lay out a full literary analysis, but it's the kind of book that warrants one. There is an oft-repeated focus on the dichotomy between disgust and desire. And a focus, paralleled by drug addiction, on the self-destructive and doom-laden impulse of youth. A focus on the most physically beautiful people doing the most repulsive things. A focus on the desire to be led battling the desire to be free, and how that leader can be a person or simple fatalism. 
 An interesting book to read and fascinating to discuss afterwards! I think you should read it and form an opinion for yourself. 
 Oh, oh! And I learned two new words! Loggia and caravanserai. 
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