Red Country is a stand-alone book, and occurs in the same world as The First Law Trilogy and the stand-alone Best Served Cold and The Heroes. This book review will be as light on spoilers as possible.
The story occurs mostly in the Far Country, which is akin in tone to the Wild West, but with a far simpler level of technology. The protagonists are Shy and Lamb, the former being a very rough diamond and the latter an elderly and cowardly man who worked on her farm. The pair find themselves trekking across the Far Country to try and save Shy's younger siblings, who have been kidnapped.
There are fewer characters of note than in The Heroes, the previous book, but this does allow a tighter focus on those who are present and works very well. Shy and Lamb, and others with whom they travel, change and develop significantly during the journey as they're confronted with hard questions and bloody answers.
The world is very well-described, and has an immersive, realistic feel. The disintegration of law and order as people travel further from civilisation towards the unclaimed Far Country and the emotional volatility of hope, despair and stubborn resilience from various quarters fits the leap of faith (some falling, some landing safely) of travelling into the wilderness for a better life.
I must admit to absolutely loving lore, and although it's almost entirely in the background the latter part of the book will be especially interesting for those who love hearing more about the antiquity of the Circle of the World.
Red Country continues Mr. Abercrombie's grey morality, which I rather like, and has an added note of poignancy. I think the tone of the book's more balanced than the previous stand-alones, which erred on the side of darkness. It's still grim and gritty, but there's a bit more yang to balance the yin.
Some versions (happily including the one I got) have a very short story at the end, written by a biographer who plays a minor role in the book. It's very much an appendix sort of story: it's enjoyable to read, but doesn't add anything substantial to the story so those without it are missing a few minutes of reading pleasure rather than any critical information or a hidden plot twist.
It's probably quite clear that I think Red Country's fantastic, but it's not quite perfect. I think that a certain cameo character could've and should've had a slightly greater presence, and that he almost might as well not be there otherwise.
So, in summary: the characters are engaging, the story is simple for the first half but has numerous twists later on and the writing is excellent throughout. It's my favourite book by Mr. Abercrombie so far, and I'm struggling to think of a fantasy I like more.