First off, if you haven't read Sea Dragon Heir yet, what are you waiting for? Go, read it. I'll wait.
Back? Good. The Crown of Silence continues the story begun in SDH. The first half of the novel overlaps the events of the first book, revealing what was going on in other areas of the world. The second half is a true mythic Quest with all that that entails.
The characters are well developed and for the most part sympathetic, but as with all of Storm's characters these are not perfect people. You will find yourself at times wanting to reach your hand into the book to thwap them on their collective heads for being idiots... but when you think about it, how would you handle the situation they find themselves in?
Another area where Storm excels (and sadly many other fantasists do not) is in the depth and resonance of her magical system. It is not some "point/zap/you're dead/you're a frog" amalgamation of fantasy cliches grafted on to the story, rather it is the story. What these characters are doing, how they are growing and evolving, is a direct result of the self-discovery involved in learning. As several characters state: "Learning is better than knowing."
I don't want to reveal too much of the plot, but I feel I must state that a portion of the book does deal with the consequences of surviving a traumatic rape and that two of the major characters are involved in a same-sex relationship. To me, these things add to the weight and reality of the book, but I realize that for some such subject matter is a determinant factor in what you read. I still recommend the book even to those people, though, as the handling of both subjects is superb for the genre, but if you're looking for another Harry Potter this is not the book for you.
As to the book itself, Tor did a great job on this one. Everything from the jacket art to the binding is top-notch. This is definately not one to wait for paperback on.