Flatterland: Like Flatland, Only More So
An okay introduction to some non-Euclidean and non-3-dimensional spaces, but it was somewhat flawed. The I didn't care too much for the characters (as others have noted, they really had no motivation), and there was too much uninspired stage-setting at the beginning, in my opinion.
The explanations of the concepts early in the book were entertaining, but I found they were rushed toward the end, and some of the puns/jokes ("Hawk King") either fell flat or were driven into the ground.