His writing style is a poor fit for Warcraft. His writing comes across as trying to further his own characters ('Rhonin is a maverick!' 'But he's our only hope.') with no regard for the lore characters involved. Warcraft also has a history of strong female leads. Jaina, Sylvanas, Alleria, etc.

Knaak seems to love him some weak females. Sylvanas and Alleria are sisters. The Windrunner family. Both are obviously very strong female leads, who can stand on their own. Sylvanas leads the Forsaken now, even. Knaak created himself a third sister (Vereesa), which was ogled and manhandled all through Day of the Dragon, and despite her claim to hate humans, Rhonin was the dreamiest guy in the world and then they did the nasty. And then Vereesa spent the next three Knaak-written books pregnant and barefoot in Dalaran with -gasp- twins! There have never been half elf twins before! :O

My list goes on, but we can sum it up this way: Knaak is an old school fantasy writer. He clings to old school pulp fantasy ways of writing. He's the kind of fantasy fiction that the genre got mocked for, for so long. Warcraft broke out of that in a lot of ways (though not all of them) and Knaak took all of that a step backwards and plunged it into stupid.