I never imagined I'd be as enraptured reading about a square describe his universe (and the ones outside it) as if I were reading an account of an astronaut or explorer (Columbus) describing a strange, newly-discovered tribe or planet.
After I adjusted to the "old timey" speak, it became easier to read. I enjoyed reading about their society, and the Colour war, and all the made up conventions by which Flatland worked. I felt very sad about the ending, and had remind myself that I just read a story about what were essentially anthromorphized shapes and solids! So I'd say it was a great yarn, that I got caught up in it like that. Would recommend it as supplemental reading to high school students taking up Geometry. It's a quick read. I finished it in less than 2 hours.
And the best part: this can be read for free at Project Gutenberg: http://www.gutenberg.org/cache/epub/97/pg97.html