(See my review of the first Virga book here.)
On the whole, I think this was a more well-rounded book than the first one. The basics of the world are already established, which makes the world-building aspects of this one less overpowering (though still fascinating, as we get a couple of glimpses into the past, and also the truly baroque societies which clutter Spyre, one of the oldest pieces of artificial land in Virga). Venera Fanning becomes a rather more sympathetic character in the course of this tale, too, which is also nice. As for plot, it's rather less sweeping in scope than the previous installment, but that's not a criticism. Personal stories can be just as captivating as epic ones, if not more so, and this one was very neatly done.
Still, even though the elements were more nearly in balance in this book, the ideas - the underlying concepts around which the world and its stories have coalesced - are still the real stars, and the thing is well worth reading just for the way they are explored. I think I am well on my way to becoming a Karl Schroeder fan, even if I was less than blown away by Lady of Mazes.