My first three impressions in reading "Kéthani" were: (1) this is a collection of short stories, written in the style of Bradbury's "Martian Chronicles"; (2) this is a pleasant, mellow read; and (3) these characters drink a lot.
Upon finishing the book my impression had not changed much, except I realized that for all of the book's genuine "gemutlichkeit," it was a serious meditation on mortality, religion, and ethics. I further realized that the Kéthani for all their apparent benevolence and understated drive, supported by an unspoken belief in manifest destiny, were sinister.
The sinister nature of the mysterious aliens and the underlying sense of danger only surface one or two times in the novel and are quickly ignored or brushed away through the characters' rationalizations. And yet, upon completion of the novel, the feeling remains that the humans have been tricked or duped in some way. In fact, our protagonist, Khalid, says in the final chapter that "I wondered whether to tell Sam and Stuart that we had been lured to the stars by an. . .an impostor." Further, in the epilogue, Khalid says cryptically that "the reason our benefactors selected us for the task was a little more complex than than we first thought." This is the extent of our illumination. At he end of the novel we know no more about the aliens than we did at the beginning. But this of course is the point because ultimately the book is a meditation on religion and life.
As Tolkien pointed out in his short story "A Leaf by Niggle," we are on a journey to death. In "Kéthani," however, the aliens interrupt that journey and substitute a possibility for immortality. Humans with their complex and innate capacity for religion are disturbed by this interruption and thereby have to re-boot. Some incorporate the Kéthani into their religious framework; others de-construct or react violently. The Kéthani could be angels or devils or simply higher sentient beings. We don't know and Brown does not provide an answer.
I recommend the novel but I do have a few reservations. First, the book feels like a collection of short stories. As a result there is a lot of repetition. This repetition arises from the fact that the author has to apprise new readers at the beginning of each story where we are each time he starts a new "story." Second, the author does not give you any answers to your questions for the simple reason that the protagonist does not have any answers. And since the work is a first-person narrative, we only know what the protagonist knows.
All in all, the novel was a pleasant experience; a welcome respite from the hardware of science fiction, with its incipient violence. In some ways the work is a throwback to the science fiction of the fifties and sixties, when science fiction was a place of ideas and we could easily compare the novel with Clarke's "Childhood's End," Bradbury's "Martian Chronicles," or the original "The Day the Earth Stood Still."