Confluence by Paul McAuley

If you fall into that centre bit of the Venn diagram of fans of Dune (Frank Herbert), Gormenghast (Mervyn Peake) and Shadowmarch (Tad Williams) that likes all three of those series, may I recommend (assuming you haven't already read it) the Confluence trilogy by Paul McAuley, which I've written a nice review of over at The Bookbag this week. I can't believe I hadn't read any of his novels before!