The City We Became is urban fantasy, in that it features a bunch of magical stuff happening in a modern day city. It's also urban fantasy in that it is about cities. People are cities and cities are people, and not in a metaphorical way, but in a more supernatural and literal way.

N. K. Jemisin manages to channel the spirit of New York City (where the novel's action focuses) through the novel's characters, without resorting to tired and popular stereotypes of the city and its people. While in a way the book is an ode to New York, it also doesn't shy away from some of its more dark and shameful aspects. All of this is wrapped up in writing that manages to be evocative and sufficiency casual to flow well. The book paints an engaging picture of both the real New York, and its fictional, supernatural, embodied New York.

The one complaint to level against the book is against the arc of the plot. The novel feels more like a series of superhero fights, leading up t a bigger superhero fight, with some twists along the way, and a somewhat rushed conclusion. This can, however, probably be chalked up to it being only the first entry in a trilogy, and this being what the genre is.