The best SF takes a supposition about the world ("What would happen if...?") and follows it to interesting conclusions. McDonell's setting holds together well, with a lot of details that seem like "obvious" extrapolations of present trends into the future, but she throws in some "aha!" moments as well. Just when you think you know who a character is, you discover they're not what you think... but when you consider it, who they really are follows perfectly from the setup. The pleasure of seeing interesting ideas fit together well combines with well-paced drama and relatable characters to make this a fun read.