I finished The Serpent Sea yesterday. The prose is very simple and basic -- occasionally annoyingly so -- and if I'd been reading in ebook format I would've counted how many times a character "snapped his wings". OTOH, you don't often get to see fantasy this aggressively nonhuman -- even elf/shifter/vamp/etc. stories are pretty much "humans with cool abilities" stories or "human among the aliens" stories. In Wells's books, though, we have a carefully constructed, complex, and detailed look at an "alien" species that looks, acts, and frequently thinks differently than ours, often in casual ways (not "oh, look how different he is!" but more "yeah, of course that's the way he'd act. So what?"), as well as their surrounding environment and the other species around them. So that's fun and satisfying.
This book didn't feel as desperate or... I can't think of the word... life-and-death as the first in the series (The Cloud Roads), which makes sense in context. In the first book Our Hero didn't know who he was or where he came from, and after he found His People he became engaged in an edge-of-your-seat battle for the survival of his colony and perhaps his species. In this one he has started to settle in, and although he's still often confused by colony life, he has become an accepted and productive colony member -- and this adventure is about saving their new home, not about preserving their very exitence. Nonetheless, it drew me along throughout, and aside from some Mary Sue-ness I have no major complaints.
As for the audio version, the narrator is fine -- I wouldn't call him exceptional, but I didn't find anything annoying except that he repeatedly pronounced "baring" as "barring" for some odd reason. And he did deadpan delivery extremely well ("Yeah, this is going to be bad" types of lines).
Overall I'm rating this about 3.5, which is about the same rating I gave to the first book in the series when I read it last year. It would probably be higher if it had better prose. And yes, I've gone straight to the third book in the trilogy, The Siren Depths, which promises to have an interesting storyline. These are fun reads if you like action, politics, and a lot of immersion in nonhuman life without having to wade through a lot of gore or grimdark depressing world views.