Short, unspoilery version:
It's awesome. It reminds me of GRRM's Song of Ice and Fire a lot, only without Sansa the boring, annoying parts and most of the epic elements (dragons, Others), and all the grittier and more realistic for it. The cynicism and insight in the workings of the human mind (even if the minds in question are somewhat more modern-seeming than those of GRRM's characters) are there, but overall, I'd say it's -- surprisingly -- more positive, even moral in places. So the main similarity is the general mood. And the beautifully nasty sense of humour, of course. I love that! (What do you mean, you didn't find ASoIaF funny? I thought it was hilarious.)
I personally liked the characters better as well, not only because they have far more depth to them (possibly because Abercrombie makes do with "only" six viewpoint ones), but because they mostly seemed more relatable in general.
The only things that might put some of you off are the author's apparent fascination with cannibalism and the explicit (but absolutely not glorifying) description of violence, especially torture. But I know the other 90% of you will read it for exactly that, so... *shrugs*
Longer version, with some SPOILERS:
World Building:
The world building is supremely meh. It seems like something straight out of a D&D clone, only with the non-human races taken out. Various historical society look-alikes (non!Picts, non!Vikings, non!Generic Early Modern Europeans, non!Arabs, non!Romans and non!Rennaissance Italian City States) coexist weirdly, but I must say the author uses what he has well, simply because it's mostly just a background for his characters to come from, and a scenery to put the action in front of, and it works nicely for that, with amusing little culture clashes. There are also enough jabs against the stereotypes and exceptions from them that they aren't, actually, too offensive.
Main Characters:
Logen: the book's capital-W Woobie. Who also kills people. A lot of them. But... he just wants to be a good person! Honestly! ... It simply doesn't work. At all. It's heartbreaking, really.
Glokta: most sarcastic guy since Raistlin, and I mean that as a compliment. He's also one of the most repulsive villains ever invented, and yet... such a woobie, too, sometimes. I love his chapters to bits! He is by far the most intelligent and (self-)analytic one of the cast and has most of the funny and quotable lines, too. Here, let me give you a random snippet that's pretty typical of him: "When was it exactly that I became... this? By small degrees, I suppose. One act presses hard upon another, on a path we have no choice but to follow, and each time there are reasons. We do what we must, we do what we are told, we do what is easiest. What else can we do but solve one sordid problem at a time? Then one day we look up to find that we are... this. He looked at the blood gleaming on his boot, wrinkled his nose and wiped it off on Morrow's trouser leg. Ah, well. I would love to spend more time on philosophy, but I have officials to bribe, and noblemen to blackmail, and votes to rig, and secretaries to murder, and lovers to threaten." (Glokta, in Last Argument of Kings) His commentary on things happening around him and what people are saying is even better. *loves*
Jezal: he starts out as this series' Theon Greyjoy, i.e. he's a stupid, vain, shallow asshole and you badly want to see him hurt. In contrast to Theon, however, we get to see him change and develop a huge deal -- only, he's still stupid and vain in the end, though in different ways, and seeing him hurt suddenly isn't half as much fun anymore when it happens for all the wrong reasons. A masterful piece of writing.
Dogman: I like the Northmen. They are all so... cute and quirky. (Disclaimer: not the most common description, I'm sure.) I love their chapters because they consist mostly of running around in the woods, being good buddies, and having battles, and compared to all the rest of the action, that seems like easy, wholesome fun. (Except for the part where all their fighting is pointless and depressing, but well. *g*)
West: probably the most easily likeable character for most readers. He has his flaws, but nothing nearly as extreme as everyone else, and overall, he's hard-working and competent and tries to do what's right. He's the most average of the characters, but without being boring because of it.
Ferro: I love her! She's tough and no-nonsense, knows what she wants and doesn't let her own goals and attitudes be compromised the way everyone else does. I like the way she sees through people and isn't impressed by things like pretty clothes or sweet words.
Race:
I'm not a specialist on representation of race, by any means, but the things I've found to criticise were that Ferro is the stereotypical Angry Black Woman (which, to be fair, she has plenty of reasons to be) and that she, as the only black viewpoint character, is a bit of a token POC, probably meant to counteract the fact that the main enemy nation is made up of what seem like Arabs and several black peoples they have enslaved. On the whole, all the really unsavoury characters we see are white, and the political background implies more blame on their side as well, but that doesn't make the fact that we only see the aforementioned POC Empire from the outside any less icky. The passive suffering of the black population of Dagoska also struck me as a bit questionable, but I suppose it works to show how strong a force internalised racism can be on both sides. All in all... Well, at least you can see the author is trying? I'd like to leave judgement on the matter to people with more insight on the issue than I have.
Feminism:
In the beginning, I thought this was the least feminist book I had stumbled upon in a long time. There isn't a single female character in the first 50+ pages. Turns out, they just needed some time to show up, to do it with all the more impact.
We get few women in total, but those we do get are great. Ferro and Vitari are badass fighters, but not without depth. Ardee and Catheil can fight if they must, and are defined by individual personality rather than female stereotype, as it should be. Same goes for the others (Eider, Cawneil, Terez, Tolomei). The only exception is Caurib, your standard sorceress cliché. But then, we don't see much of her, so there's not much space for characterisation.
I'm sad to say, though: the book doesn't pass the Bechdel test.
Humour:
As I said, it's nasty. Beautifully so. You can laugh with the characters, or about them, about the irony of fate, or lack of it, about plot twists you figured out, or those that surprised you, but laugh you will. Evilly. I'm pretty sure I've weirded out more than one person over these books on my daily train rides.
Morality:
At first glance, it's surprising to say this series, drenched in gore as it is, is more moral than ASoIaF, but I argue that it is. Mostly because not every attempt to be a decent person is relentlessly punished by auctorial mandate. But it doesn't mean you're in for a karmic reward, either. Fate isn't really fate, it's realistically random. Which I approve of. Doing the wrong thing isn't always strength and necessary for survival, as it is with Martin. Often, it's simply and obviously the wrong thing, and it's nasty to watch, without the machiavellic justification of "Well, gotta be tough to survive" (which, amusingly enough, is in the text, uttered by the characters, but is debunked more often than not by the events, which speaks louder than words to me). (I'd say that stems from an important difference in both authors' attitudes, but that's speculation.) First Law also does morally grey a lot better: while GRRM's characters are on a sliding scale from good to evil, in Abercrombie's, the borders between heroes and villains are almost entirely fluent, and sometimes the shift in perception from one to the other is radical enough to leave you reeling -- and yet the characterisation is never self-contradictory: they have always been this way -- you only see them differently all of a sudden. As I said, I love the characterisation madly.
Prose:
The prose is truly shiny: fluent, evocative, emotional in an understated way, and with a distinct style for every viewpoint character. Dialogue and description are also very well-balanced, and the dialogue is realistic.
Plot:
The plot is just as brilliant as the rest: Just when you think you've seen through it and start rolling your eyes, something unexpected happens -- but, and that's the clincher, not every time! Sometimes, things actually go the way you'd logically expect them to but didn't think they would because, well, frequent surprising plot twists. It stops you from comfortably trusting the author and thereby becoming bored (as sometimes with GRRM, when you just know things will go the nastiest possible way, and no exception). There are expected and unexpected climaxes and anticlimaxes, moments of awesome and moments of suck, so wildly intermixed and rapidly turning from one to the other that a) you are constantly on your toes (seriously, not one boring moment in this entire series!) and b) it seems utterly believable.
Oh, and I love the ending, all of it. It's satifying, in its realistic unsatisfactoriness. (This will totally make sense once you've read it, believe me.)
Now go, read it and be fannish with me!!! (The books are, in order: The Blade Itself, Before They Are Hanged, and Last Argument of Kings.)