If there weren't plenty of evidence against it, I'd think that the Martha Wells who wrote this book and the one who wrote City of Bones are completely different people. City of Bones and Wells' other early books are interesting and well written. The Raksura books, on the other hand, are distinctly average.
Wells has come up with an interesting world for the Raksura, so it's not a failure of invention that plagues the series (though there are weak points, like cost-free magic). Most writers get better as they age (unless they get distracted by particular obsessions), but Wells' Raksura books simply don't seem very well constructed. There's a pervasive feeling of action for the sake of plot, rather than as a result of natural character choices. For example, late in the book, some of the characters have escaped danger, and should be free to go. For no reason at all, they presume antagonism in a new set of encounters. It's clearly meant to heighten the tension, but fails because there's simply no reason for it to happen. It's confounding and frustrating rather than exciting. There are similar moments throughout, as if Wells has mysteriously lost her ability to construct credible characters and story. Because so many character actions don't make sense, the story is not very interesting to follow.
The story is unfortunately also an entry in the 'might makes right' subgenre. Most of the character relations in the book are based heavily and often explicitly on 'do as I say or I'll beat you up'. Happily for us, our hero is bigger, stronger, and meaner than the bad guys. It's a lazy and distinctly unappealing approach to character building; even Conan had a little more depth. There's a distinct racial/speci-al element to the story as well, with the Raksura treating groundlings (humans) as a distinctly lower class. There's never much introspection about this. The Raksura are simply high-handed in how they treat other species, and they get away with it without a second thought. For example, one 'waterling' who answers their questions (a bit grudgingly) is dumped far out of his way because ... why not, if that's what the Raksura feel like? Equally unappealing is the double standard the Raksura use. When they do something, well, they're good guys. When others do the same, it's shocking! There's not much character recognition of this, even when the parallels are painfully obvious.
There are other inconsistencies in the story and setting. They'd be minor issues if it weren't for the above, though there are a few key points that simply make no sense, including one related to the core of the story - the special seed they spend so much time searching for.
I used the word 'lazy to describe the writing. Perhaps thats harsh, but I'm not sure what else to think. There's a lot good in this series, but so many flaws that it just doesn't work. Yet Wells' early books were quite good. Perhaps she's under time or other pressure. Whatever the cause, the result is far from the skilled presentation I expected. Some people clearly like the series, but my feeling is that if you loved City of Bones, you'll be pretty disappointed by the Books of the Raksura. The title, by the way, is misleading. Theres a sea, certainly, but little in the way of serpents.