This should be 3.5 stars. I would recommend the book generally to folks who like history and adventure, but I had a few issues with it myself.
On one hand, I enjoyed the premise of this book very much! It's a fun archaeological adventure, although it is set against some devastating history, so maybe “fun” isn't entirely the right word. [slight spoiler] I wasn't wholly satisfied with the way the riddle resolved in the end: it was clever, but it didn't click perfectly into place with the way the story had been told.
My main issue, though, was with the dialogue. It's snappy in some places, but too often it rehashes information we already know, or reads as the characters telling each other lots of facts they both already know. While I appreciate that all the main characters are very knowledgeable, I think the dialogue editing could have been tighter. In fact maybe having a main character who wasn't so knowledgeable would have made this flow of information more natural.
Also – and this is a small thing, but it alienated me personally as a reader – as a historian myself, I was a little baffled by the historical texts in the book. They read in a very modern way. I wasn't sure if this was a conscious choice by the author, or if in the world of “The Queen Jade” history is different than in our world, or if this was accidental. Despite the characters bantering about details of the documents, the issue of these modern voices was never fully dealt with. And while I do love those historical characters' stories in the book, I just needed their eccentricities (relative to their respective time periods) to be addressed (or written slightly more subtly) in order to keep myself immersed in the story.