The Canadian biologist and SF writer Peter Watts, in the somewhat sour and defensive afterword to his selection of short stories Beyond the Rift, comments ruefully on the terms he finds often applied to his work: dark, paranoid, dystopian. (Sour isn’t there yet although I guess I’ve just added it to the list.) But, as he points out, “There’s wonder here, too: a diaphanous life-form big enough to envelop a star; mermaids soaring through luminous nightscapes on the ocean floor; a misguided Thing whose evolutionary biology redeems Lamarck.”
The best stories in this selection are the ones that give scope to that sense of wonder. When Watts focuses on the near future, or the earthbound, or the topical, his characters are often one-dimensional ciphers; and there’s always an undercurrent of aggrieved resentment, of sour disappointment in how inevitably awful humanity’s behavior will be. 
But when he gets out into deep space or deep water his stories, paradoxically, get a chance to breathe; taking time with the setting, and the mechanics of surviving in it, he lets his characters out from under his judgement, and once they’re free they consistently surprise the reader and themselves.
So the standouts here are the stories set in space (“The Island” and “Ambassador”) or in the undersea milieu of Watts’s Rifters trilogy (“Home” and his first published story, “A Niche”). I’d previously read the Hugo-winning “The Island,” about a mother-and-son team of wormhole builders who come upon an intelligent Dyson swarm, and found the downbeat ending to be a gratifying, surprising tonic. “The Ambassador” is less expansive but similar in tone, while “A Niche” is an expertly paced and constructed story, with the kind of ending that makes you laugh in delight at how well the author has set it up and how little you saw it coming.
The characters in these four stories are all edgily, uneasily posthuman, brutally bioengineered for the harsh environments they explore. Their existence is more or less a torment to them, sometimes due to neglect of the human sensibility trapped within the engineering and sometimes due simply to past trauma (there’s a substantial amount of past trauma in Watts’s work, often child abuse).
“The Things,” meanwhile, possibly the best-known of the stories here, is a retelling of John Carpenter’s 1982 film The Thing from the alien’s point of view. It’s clever and enjoyable, a thorough exploration of a truly alien mindset. And it does a great job of making the alien sympathetic — but honestly don’t be fooled:
That is not a life-form you should be rooting for.
Other stories are less effective. Watts, the son of a Baptist minister, doesn’t like Christianity — in the afterword he calls it believing in “an invisible sky fairy who sends you to Space Disneyland when you die,” and the atheist clichés there give you a sense of his not-terribly-nuanced thinking on the subject. So “A Word for Heathens,” and “Hillcrest v. Velikovsky” spend some time on that. There’s a handful of stories that extrapolate modern technology to pretty modest results (“The Eyes of God,” “Mayfly,” “Flesh Made Word,” etc.). A different reader may get more from these ones than I did, as I tend to find this sort of story the most inessential sub-genre in SF.
“Nimbus” is about, uh, angry clouds.
These stories, as well as a few forgettable others, may spring from Watts’s frustration with modern humanity but they don’t play to his strengths. And I suspect he knows this: it’s probably not a coincidence that his novels take place in the same settings as his strongest short stories. So far, of the novels, I’ve only read the truly magnificent Blindsight, but the whilequel/sidequel Echopraxia, due to hit the shelves in August, is already one of my most anticipated reads of 2014; and based on “A Niche” I’m pretty eager to get to his Rifters trilogy.