This satire was written in the 19th century, as is plain with the elaborate style of writing, which at times can be a bit tedious to follow.
The novel [if it can be called that] has a mathematical aim, steadily guiding the reader into understanding the geometric concepts of different dimensions. Written by a teacher, it appears to me to be aimed at a young audience, as the structure of the plot shows. Flatland seeks to describe and explain the conditions of life in 0,1,2,3 and 4 dimensions, using a parody of different classes to describe the characters.
Guiding us through these complex ideas is a certain A. Square, who inhabits Flatland, a country of only 2 dimensions. A member of an educated class, he makes clear the stark differences between his world and ours, all the while forcing us to ridicule the social structure of those days.
I guess it is a good read if you're about 10 years old, but anyone older than that may consider the tone of the book a bit patronising. Interesting all the same, but perhaps dimmed with a lack of context [i.e. a bit outdated].