For me are two things: the emotional moments and the twists.

"TAKE EM ALL", "I dinnae let go", "Wanna play blocks", "You're not Durkon at all" are on my top10 best emotional climaxes ever, in any media, be it movies, games, books, series, you name it. It's incredibly satisfying to read and to see those parts of the story unfold. I try to bring more people to read OotS just to see their reaction when they get to those parts.

And the second thing I enjoy the most are the twists, like this one. I remember being so utterly pissed because the paladins were wiped in a single strip, and the revelation that they were actually there as reinforcements was extremely well crafted.