Despite my qualms about Planetfall (and I've got quite a few), it is at least a complex novel with an extremely relatable, well-rendered protagonist, and that is more than most novels accomplish nowadays.
Renata Ghali is the most highly skilled molecular printer engineer in a colony of humans living on an unspecified alien planet. She and her fellow colonists have been living and thriving there for twenty-two years, having left Earth in the wake of the chaos caused by overpopulation and ecological instability.
And that was not the only thing driving them to this particular planet. Years prior to their departure, Renata's best friend from college, Lee Suh-Mi, suffered a coma, and upon waking discovered herself strangely drawn to a particular Earth-like planet that had recently been surveyed with unmanned interstellar ships.
Upon this particular planet lies a structure that Renata and the colonists call "God's city," but which physical description constructs as a hybrid of the Yggdrasil and a Cthulhu monstrosity. The novel's tension is derived mostly from waiting for the events surrounding the colonists' arrival to be revealed in order to help explain the reverential cult of personality that has grown up around Suh-Mi, and explain why she's now living alone at the top of God's city.
The largest of my qualms with the novel is certainly that aforementioned element of the mystery genre–the intentional holding back of key information relevant to bring the larger themes into context. In a mystery novel, the reader doesn't require the context of the missing information to make sense of the environment and social dynamics, as those typically occur in a realistic setting. In Planetfall, the withholding of the crucial information is merely frustrating.
At first, I also found Renata's characterization suspect. The narrative is told in the first person. Why did Renata seem to be avoiding thinking about the events that would enlighten the reader? It became clear as her personality developed that she had very, very believable reasons for not wanting to. Well-realized characters make a novel shine, and Renata does just that for Planetfall. Her pain and anxiety are very human, and it is largely on the strength of her character that I can recommend this novel.
As for the other characters... not so much. Carmen seems to be merely a flat anti-Renata, and Mack makes some decisions toward the beginning of the novel that didn't line up with his character as depicted in the reveal, but I found Sung-Soo the most problematic character of all. For all of Renata's mental challenges, I trust her enough as narrator to accurately relate the facts of other characters' behaviors. If Renata's view of his behaviors is to be trusted, then Sung-Soo threatens basic believability, or there is something wildly wrong with him mentally. I physically groaned at his mini-reveal.
And then there is the highest level to consider, that of what the novel, as sf, can teach the reader about humanity and human society. I found this vector troubling. Planetfall falls into the common science fiction trap of painting religious belief as the result of intellectual weakness and emotional insecurity, its sole utility as merely a lever for the power-hungry to exploit. And I believe it's this vector from which all of Planetfall's troubles emanate. Since the novel can't have a nuanced dialogue with the topic of religious belief, since its goal is to merely denegrate it, then characters must behave strangely, and Renata must paint black-and-white pictures of "what would have been" if they hadn't been stupid enough to believe.
For all its foibles, Planetfall is certainly an engaging novel with an intriguing protagonist and enough substance to prompt a discussion of ethics, though I question how far the novel could take such a discussion.