Well, that was a very good, action-packed fantasy trilogy. It had great dialogue, terrific characters, and moved along at a consistently quick pace despite the now-typical girth of the novels themselves. I'll attempt to elucidate the reasons why I think fantasy fans definitely should read this series, and also why it wasn't the best thing I've ever read.
First of all, the good. As I said, the dialogue is quite strong, very funny. It impresses me that Abercrombie can write such savage action sequences and yet his books are replete with dialogue-driven comedic moments. Especially funny are those moments involving the crippled torturer Glokta, who tortures because torture is now the only thing he has left, and whose brutal sarcasm cuts almost as deeply as the many blades which are the tools of the trade he despises. Glokta's humour is what makes him easily the most entertaining character in the entire series, and this series has a plethora of characters with a high degree of entertainment value. As I noted in my review of Before They Are Hanged, characters are clearly what Abercrombie does best, so no need to belabour that point here. No, what was more significant about the third entry in the First Law Trilogy was the length to which Abercrombie went to subvert common fantasy tropes. He toyed with them all before putting them to death; the hero's redemption, the long unrequited love finally consummated, the benevolent wizard saves the world, the swordsman becomes a king, the betrayed man achieves his sought-after vengeance...there's probably a few more I'm forgetting. There are few happy endings here, and that's as it should be, as all the characters lived by the sword, literally or figuratively. Though few of them are content with their lot, many of them understand towards the end that the sword is a terrible thing to live by.
The series had some flaws, or perhaps it's just one major flaw. I'm not one of those who was depressed by the tone or put off by the perceived "nihilism" of Abercrombie's purported worldview - in fact, I don't grant the premise that Abercrombie believes that everyone is shit (in fact, I think that's a pretty shallow and facile reading of the series). No, my issue with the series, and this book in particular, is that it felt like Abercrombie wanted to do a lot of exploring and worldbuilding but didn't really have time to because he needed to deal with a bunch of obligatory fantasy plot threads. Now, as I said, he messes with the standard expectations of fantasy, but he still has to write within these stereotypes in order to turn them on their heads, if you see what I mean. For example, the second book in the series was largely a quest narrative featuring an adventuring party made up of a barbarian, a woman warrior, a noble swordsman, and a wizard. Quite cliched. Yes, he turns it around on us, but it took a whole book of a fairly standard-fare quest to do that. It felt like if Abercrombie weren't quite so busy thumbing his nose at what was expected of him he could have done something truly remarkable rather than what this series was.
Which was, all things considered, still quite good.