Anduin Wrynn: Few times I wanted him to just shut the hell up. Seemed quite whiny for a large portion of the book. Though I guess that can be attributed to his character growth throughout, as I didn't hate him quite as much towards the end.
Magni Bronzebeard: Really liked this character, which is unusual for me and Dwarves. It seems to me like they didn't necessarily kill him off as much as they wrote him out for the time being. After all, we know how death doesn't quite stick when it comes to Bronzebeards.
Moira Bronzebeard Thaurissan: Portrayed very well in my opinion. I loved hating her. Acted exactly how I would expect given her situation and personality.
Varian Wrynn: Didn't really like the Varian/Lo'Gosh split personality thing. Glad it didn't take up very much of the story. Thought his infiltration of Ironforge with the SI:7 agents was particularly badass.
Drek'thar: Don't know much about his backstory other than being the leader of the Frostwolf clan and teaching Thrall in the ways of Shamanism. Thought it was kind of sad that he was made out to be some senile old orc for most of the book.
Garrosh: Was Garrosh. Not particularly fond of him, even as an anti-hero. The character is just too one-dimensional for my taste. I'll go into it more when I get to Cairne.
Thrall: Where I felt the meat and bones of the story was. Azeroth was suffering, and Thrall felt it was his responsibility to fix it. I think his decision to appoint Garrosh as leader of the horde in his stead was completely ridiculous, however. Using the excuse that people like Saurfang or Cairne or even Eitrigg were just too old felt like more of a cop-out than anything else. Especially after Cairne proved in battle that he was, at the very least, Garrosh's equal.
I felt myself wanting to skim through parts of his training in Nagrand, but I'm glad I didn't. I thought the visions of his past and how they tied into the different elements was interesting.
Aggra: The relationship forming between her and Thrall felt forced, but I'll withhold judgment until there's more development. I suppose that in itself could be construed as a negative, though.
Cairne: Oh, Cairne. You old Bull. I thoroughly enjoyed Cairne's perception of Garrosh during the celebration after the return home from Northrend, and how it evolved during and after Garrosh was appointed Warchief.
Garrosh's decision to make the duel with Cairne a fight to the death made no sense to me. I understand that he felt his honor was besmirched, but I don't think that's any reason to deprive the Horde one of the greatest leaders it will ever see.
Magatha Grimtotem: Again, deliciously evil. However, I feel like they could have gone into more detail about why she was doing what she did. Maybe that's just me, though.
Baine Bloodhoof: Another well-written character. I look forward to seeing where they take his story in the future. I especially liked the interaction between him and Anduin later on in the book. Which reminds me...
Jaina Proudmoore: More of the same, really. We get some development in that we see her acting as somewhat of a mother-figure to Anduin. Other than that it's more self-doubt and regrets about the same old shit (Arthas, relations between Horde and Alliance, etc...)
I felt that Vol'jin should have had more to say about the situation in the horde, but from what I understand that will be covered more in-game.
Also curious as to the whereabouts of Malfurion Stormrage with everything that's happening to Azeroth. Granted I couldn't bring myself to finish Stormrage, so I don't really know what he's been up to since coming back.