I've read the Jaina novel.
It's probably going to be a little spoilt now anyway as you know how Theramore ends and have probably picked up some further info while playing.
It all felt pretty safe and simple with a bit of a odd twist near the end. You only have to look at the Amazon reviews though and it's quite clear a lot of people enjoyed it.
The characters were pretty much acted how you would expect. Jaina acts to protect her city while Garrosh is quite cunning until he throws a temper tantrum later in the book. The division within the Horde grows and you will be introduced to some new characters.
I can't really go further without spoiling it. I enjoyed the book but I'd hardly say I found it utterly compelling.
I've mixed feelings for Knaak. I certainly felt the Diablo's Sin war trilogy dragged on. Although for that universe I'd just advise getting the Book of Cain anyway as it summarises the history of sanctuary. /Off topic yay.