The Way of Shadows was the meh in my honest opinion.
I mean, what's up with the nonsensical attitudes (like a general being spared the murder of a king that way. WTF?), trying way too much to be gritty, love just for the sake of it, the fact Brent was unable to seamlessly fit curses in normal talk, and the inconsistent magical powers. I don't like reading about a bunch of supermen, specially when their powers show up only when it is convenient.
Anyways I still bought the whole trilogy, beginner writers deserve our support (meanwhile I pirate every single game! Weee!) and felt it was worthy my time at the end, the plot was good even with all these flaws.