My introduction to Daniel Clowes was actually for a college assignment--one of my first college assignments, in fact. (I remember thinking something along the lines of "Man, art school is awesome...they make you read comic books.") I recall the teacher saying that he found it so remarkable that a middle aged man had captured the voices of these two teenage girls so convincingly.
It was probably one of the first comics of its kind that I'd read (other than maybe Evan Dorkin comics like Milk and Cheese or Dork, although that's still not quite the same type of storytelling).
While Ghost World is a bit more realistic than some of Clowes's other work, there are still some random bizarre details, like the girl with the giant goiter on her neck (more like taking over her whole face).
Another great detail is all the self-referential "Ghost World" graffiti around the town.
I kind of love how these girls are total assholes, even though they do grow up a bit by the end.