I just finished "Mother of Lies," the second in a duology by Dave Duncan (no relation), and I can wholeheartedly recommend both of them. In general, the story is intense and intriguing, with some enjoyable twists, realistic and flaw people, and - again - the sense that what occurs is less a plot as an organic exploration of events. Characters who have been hinted at and mentioned throughout the first book finally surface in solid portrayals. And once more, Duncan (no relation) manages to pull off showing an event I knew was coming while making it effective and surprising.
I did have some quibbles. One romantic relationship in the story just seems to happen out of nowhere. There were a couple bits in both dialogue and internal narrations that seemed like modernisms and thus out of place. One of the main antagonists was degraded in such a fashion that I thought it did a disservice to the entire storyline. I didn't want to see her reduced before the final showdown. In part due to this, in part just due to portrayal, this same showdown felt anticlimactic to me (though it wasn't the only showdown in the book, and the others were superb). One plot-thread was never resolved. And though the unusual physical design of the world was touched upon, it didn't seem enough - particularly as the book ends with an appendix discussing how the physical geography would (not) work.
That aside, I recommend these two books heartily. They're well worth the read.