Let me start by saying that Traitor Spy isn't anything like the The Black Magician and it never convinced me or intrigued me as much as those books did. The main problem in the Traitor Queen is the characters we get to follow. They are just not interesting enough and the characters we'd actually like to hear more about, don't get as much space in the book. Dannyl's storyline was interesting every now and then, but ended quite disappointingly. I expected him to do more when the war finally happened, even though he was the ambassador.
Lorkin was mostly boring, and he went on too much about Tyvara being so important to him. It was interesting to see what happened with the gemstones, but in the end even that seemed quite a disappointment and I was actually wondering what would happen to the wasteland.
The "final battle" ended way too easily for my liking. I kept thinking things were going too smoothly for the Traitors, expecting the Sachakan to turn things around but that never happened. The battle was over so soon. It was however fascinating to read how the slave system was overthrown, but Canavan could have done more with that. We never really saw much about the slave rebellions.
And, unfortunately, we don't get enough Sonea, and Sonea isn't anything like the important heroine she was in TBM. But one of the things I did love was the developing relationship between Sonea and Regin. Regin of all people! Canavan actually handled that really well. We knew him as the bully from TBM, but I would never have expected his character to develop the way he did. I was pleasantly surprised and he was one of the people I would really like to have seen more of. Unfortunately we didn't get that either.
Yes, it was a good book, I liked where it was going. But at the same time there were too many things going on, and none of these things were developed in a way that would make them very fascinating. A lot of likeable and interesting characters didn't get mentioned in the book as much as they should have been, and a lot of uninteresting persons were dwelled upon too much. One of the most disappointing things was that Cery didn't get the ending he deserved. I loved him in the TBM, but in Traitor Spy all he did was moan about how old he was now. He should have had a heroic ending at least.
If you have read TBM, I would still recommend you to read Traitor Spy but you should not expect it to be of the same level. I usually can't put a book down if it's good, but I could easily lay Traitor Queen aside in the evening. That's not a good thing. At the same time, I did want to finish it, I enjoyed a lot of the storylines, there were some very interesting things happening, the conversations were usually really good, and we got to follow some of our beloved characters from the previous books again. But Canavan could have done much much more with it.