TL;DR version: It's a fantastic adventure story - new worlds to discover, fame and glory and risk and death, unknown pathogens...greedy corporations, sex...
Dave Duncan has a gift for creating planets. He starts with the orbital parameters, and ends with the smell of the place: correct, plausible, yet creative.
Corporate politics, gender politics, biology and pathology - again, plausible, well-constructed. He doesn't *need* to write chapters on backstory, a few well-written sentences do the trick.
The problem with this book, in my opinion, lies in its handling of social commentary. Oh, the characters are well-done, even if a couple of them are a bit 2-dimensional, but that is *not* a writing problem - we're in Seth's head, and we see the world filtered through his eyes, and he can see the world as 2D from time to time.
So, the social commentary:
Firstly, I have to give Duncan props for his courage and his internal ethics-compass. I was not expecting this, and when I found it, it was a surprise, and a good one.
Most mainstream SciFi writers, especially straight men, will not handle some of the social issues brought up here - gender politics, fluid sexuality, cis and trans identities. It's done with some mild amounts of clumsiness, but the *message* is strong and clear. Heart's in the right place, at least.
I've seen it done better - by Bujold, McCaffrey. Mostly women writers. Because to write about it, you must sympathize, if not empathize. And sympathizing means truly *seeing* it. Many men don't, you know, especially in the Aerospace industry, STEM fields - the sexism, the requirements for conformity. I've seen colleagues sit down at lunch and just *watch* the subtle harassment of one of our own, and when confronted, the response is often "well *I* didn't see it as harassment", with the unspoken addendum of "Man up, Aldous, it wasn't a big deal, *she's* not making a fuss, why should you?"
So kudos, Mr. Duncan, for seeing it.
The problem in this case is that the sensitivity and intelligence of our MC, Seth, is at war with his testosterone-driven fight-or-fuck Wildcatter nature. Throw in a few dashes of post-adolescent young-man-fantasy-fulfillment, and you get a book with rampant contractions. Seth sympathizes, but doesn't empathize. He's fearless, but prone to falling into the same cultural tropes as any other action hero.
Then he marries a Herm, with a full-femme thrown in there to keep the balance, because Duncan sympathizes, and is creative, both socially and scientifically, but he still cannot internalize the world he writes about.
And that's quite OK, because it is leagues and leagues better than his competitors.
Oh, and the prions. +1 star for the prions.