Fiction writing is generally strongest either in plot, characters or setting. In general fiction it's most likely plot. In fantasy (which includes sci-fi) it's generally setting. And in "literature" it's usually characters.

These Gormenghast novels are really strongest in characters despite the massive castle and as such for being categorized as fantasy it's pretty unusual, ultimately though it's just miscategorized I think. Not that I like to go on about categories. But the insight about fantasy-setting, general fiction-plot, literature-characters is worth noting.