I actually finished this book a few weeks ago – I read it in one or two sittings. This is, in my opinion, the best Alex Verus book so far (although you do need to have read the previous books in order to know what’s going on).
A weakness of previous books was – in my opinion – Alex’s isolation. Pretty much everyone in his world was against him, and, for the earlier books, the secondary characters (e.g. his apprentices) were much less powerful than he was and featured more as people Alex needed to protect than true comrades. In Hidden much of that appears to be changing. It’s no longer quite Alex-against-the-world (which gets old after a while), and I think it’s a vast improvement because the greater participation of other characters allows a richer story.
And, of course, we get to see much more of Anne – who is one of my favourite characters – and learn more about why she is the way she is.
I’m looking forward to the next book in the series, Veiled.