I've recommended these books a number of times here and elsewhere. He develops an incredibly interesting world, sets a breakneck pace in the 2nd and 3rd books, and delves deep into a number of philosophical themes that are very uncommon in standard fantasy. For me, great books are ones that can inspire reactions and emotions in me. If I can actually 'hate' a character. No not the standard baby raping, dog eating butcher that we're 'supposed' to hate, but everyone secretly thinks is cool. But someone you despise as if they were a real person who just took your job, stole your girlfriend, wrecked your car, burned your house down and canceled your HBO..that kind of hate I had/have for the Kelhuss character.
And that's reason #1 (of dozens) why I know that these are great books. I don't want to spoil things, but there are tortures too gruesomes and fates unfit for man, woman, and child that I wished a thousand times upon that character.
I love the questioning and conflict between free will and determinism within. Kelhuss's convenient recognition that if the fate of these peoples are already controlled by circumstance (history/culture/upbringing), than it's wrong for him to subvert their will to his own needs (in his mind). His understanding merely by glancing at a branch and twig that not all paths and ends are equal. There are layers upon layers of shit in these books. They could be diassected for a dissertation. And they're still a great, fun read even if you don't get into that shit.
Further, these books really only scratch the surface of this world. There's more than enough remaining mystery to get you clamoring for the next trilogy.
To put it in perspective how much I despised Kelhuss, I was cheering for the young Byzantine prince/emperor.