All Intensive Purposes

Eric Rosenfield has some thoughts about round and flat characters:

In his book, Aspects of the Novel, E.M. Forester separates characters into "round" and "flat." The difference is deceptively simple; a flat character is "constructed round a single idea or quality"; "The really flat character can be expressed in one sentence such as 'I never will desert Mr. Micawber.'" The round character, on the other hand, is a character "capable of surprising in a convincing way"; "It has the incalculability of life about it—life within the pages of a book."

Michiko Kakutani and others seem to presume that "round" characters are good and "flat" characters are bad, but of course a great many great writers employ "flat" characters.

Tip o' the cap for this to Ya Sam.