Joan Vinge's 1981 Hugo-winning novel dances on the line between science fiction and fantasy. On the one hand, it contains the elements of space opera: faster than light communication and travel through black holes to a galactic empire, an empire that is living on the shreds of its more advanced past and in which conspiracies abound. There's also some hints of planetary romance, especially when we find how deeply Vinge has worked out the history and culture of the planet Tiamat. But through all that there remains strong strains of fantasy as well—young lovers swear their love for one another and then are driven apart by their separate destinies. There are even magical creatures like sibyls and merfolk. Fortunately, Vinge is able to bundle these threads together into a thoughtful story that emphasizes the power of individuals even in the galactic or worldly settings that inform the genre of speculative fiction.
Tiamat orbits a black hole that is used by the remains of a faltering galactic civilization to transport ships from other regions to Tiamat. For reasons that the novel doesn't make entirely clear, the black hole is only usable for 150 years before becoming unavailable for the next 150 years. Over generations, contact with other races has led to a bifurcated culture on Tiamat—the Winters, pro-technology and forward-thinking, rule while the black hole can be used for transport, while the Summers, agrarian and stable, rule when the rest of the cycle. Tiamat appears to offer nothing of any importance to the rest of the culture they are a part of, except for the blood of a race of creatures called mers that are never fully described but seem to be a mix of dolphins and merpeople. Their blood is used as an anti-aging agent, and its regular use appears to guarantee near immortality. As a result, during the winter phase, the other races of the culture exploit Tiamat shamelessly, all in an effort to get mer-blood. But when Summer comes, the other races leave and destroy all their technology, throwing Tiamat back into a bronze age and giving themselves a ridiculous market advantage when they return with the coming of the next Winter.
The novel opens with Tiamat approaching the end of the Winter cycle, and the current Winter Queen, Arienrhod, setting in motion a plan to ensure some sort of continuity so that Tiamat will no longer continue to be exploited with the next Winter. Her plan involves ensuring that a clone of herself wins the throne of the Summer Queen, mistakenly assuming that a clone will grow to think and feel as she does. Of course, Moon, the sole surviving clone doesn't, since she is raised as a Summer and has no idea of technology or anything about court politics.
What follows is really two stories: Arienrhod developing her plan in the face of defeat when she thinks Moon has died, and Moon growing up and learning about the culture Tiamat is a part of. Over time, she does become as indignant about Tiamat's being exploited as Arienrhod already is, but because she actually makes it off-planet, she also learns more about the cause of the exploitation. As you might imagine, given the emotional connotations of "winter" and "summer," Arienrhod is set up as the villain of the novel, even though she and Moon share the same goal and outrage. For great swaths of The Winter Queen, Arienrhod is presented as ruthless and driven, characteristics that dramatically oppose Moon's pastoral calm and surety. And taking a step back from the narrative, the real difference between the two of them is their methods for attempting to right the wrong they perceive in their planet's and their people's treatment. I would argue that during those same segments of the narrative, Arienrhod is a remarkably sympathetic character, using the tools of the trade she has been brought up in—politics—to achieve a noble end. When she is compared to Moon, of course she looks bad, but that same comparison also makes her look that more sympathetic—for in Moon, we can see who Arienrhod might have been had she not been forced to grow up in the court of the Winter Queen.
There are a number of minor characters, a lot of whom interact with both Arienrhod and Moon. Strangely, there are no really happy characters in The Winter Queen; no one, not even the offworlders who exploit Tiamat are satisfied with their lot. Typifying these characters is Sparks, Moon's "pledged." Born of an offworld father and a Summer mother, Sparks straddles the line between the pro- and anti-technology stances of the Summers and Winters. He and Moon swear their love to one another at a young age, before they have any exposure to the world outside their little island, even though Sparks pines for a different life and chafes at the restrictions placed upon his people. And when they are exposed to the rest of the world, indeed to the galaxy, their juvenile beliefs are shaken so badly that Sparks loses his. Eventually, believing Moon to be dead, he finds his way to the capital city where Arienrhod appears to delight in corrupting him to her manipulative ways. But their moments together make it clear that as much as Arienrhod is hardening Sparks up for a different life, Sparks is softening hers in another indication of who she could have been.
While the characters are not happy, they are sympathetic; Vinge does a very good job of developing the minor characters into interesting reflections of and refutations of the galactic culture and individual races they rise out of. And by the end of the novel, those characters that survive are on the road to happiness they didn't know they could have. The conclusion of The Snow Queen rounds out the fantasy threads of the novel—the questor successfully fulfills her mission and receives all that she is due. There may be some question of her eventual success down the road, but there are hints that she has the strength and the people around her to bring Tiamat out of the technological backwater it has been relegated to.
If The Snow Queen were published today, I'm not sure it would not be considered a "YA" (young adult) novel. It seems to have all the characteristics of those types of novels—straightforward if not simplistic writing, youthful main characters coming of age, and some despair along the way to a generally happy ending. This is not meant to denigrate the novel in any way, just to further characterize it for readers uncertain if it is the type of book they would enjoy. There is not a lot of depth to The Snow Queen but there is a lot of breadth.