Dense, dark, satisfying, with interestingly flawed characters (literally, the Dregs of their mercantile society) and a plot that keeps twisting and ambushing the reader till almost the very last page, Six of Crows divided our group. Those who loved it, LOVED it (I was in that camp). There were some who didn't get on with it -- put off by its length, or the initial profusion of characters, or who just don't like fantasy that much. And that's fine. Big meaty fantasy stories aren't for everyone. But Bardugo hits a YA sweet spot that doesn't mollycoddle its readers. My 14 year old tells me that the series set in the Grishaverse (there are at least five more books, and a movie on the way) is huge in her demographic, and I can see why.
Six of Crows reminded me very slightly of the Chanters of Tremaris books: the types of magic are similar, though there's no singing involved, and the world also has echoes of Tremaris, insofar as both universes have echoes of our own planet. Ketterdam is a cousin of Gellan; icy Fjerdan is a little like Antaris. But where Tremaris is a fairly gentle world, comfortable for upper primary/lower secondary readers, the Grishaverse is squarely YA, with a hefty body count and some pretty adult darkness. It's Tremaris on steroids and sleeping rough. A book, and a world, to sink your teeth into.