This one never clicked for me. The problem is possibly on my end -- I read it while tired. But, for whatever reason, the story felt overstuffed. There are four narrative threads running through most of the book (following Chen, Zhu Irzh, Inari, and a newly-introduced shaman). There are two Big Bads who seem to be independent of each other. There's the occult city of Agarta, the White Pyramid, a talking book, a time-travel spell, a terra-cotta army, a quick glimpse of Rlyeh, and -- well -- a bunch of other stuff.
It was too much stuff. Normally I'm all about the "jam more in" approach, but the climaxes stepped on each other's feet rather than building bang-bang-bang into a torrent of awesomeness. Maybe this wanted to be two novels; if so, neither of them got developed the way I wanted.
I don't mean to complain too much. It's a fun book and plenty of cool stuff happened. I don't expect to give up on the series (assuming there are more forthcoming), but this entry was a little weak.