“Good” characterization begins with full dimensionality and detail. Stereotypes are not interesting to follow through a whole novel. A distinct personality and character, whose mental, emotional, ethical, and spiritual features are artistically expressed, both by mental reaction and consistent behavior, can not only carry a comprx plot, but can stay with a reader for life. When the author places a good character (“good” meaning three-dimensional and believable) in a setting that allows for a plot in which the character gets to act on, not just talk about, his environment, is the linchpin to such memorable novels as Moby Dick, Crime and Punishment, Pere Goriot, and Don Quixote, where the character both acts out the action of the plot and, at the same time, represents an abstract idea, separates a “page-turner” or a pulp-fiction novel from a classic that adds a character to the population of informed readers. Secondary characters, too, display these same traits, in first-rate novels.
If by good characterization you mean a good detailed charecter then I feel its very important but the main thing is the plotline. I actually just read a book the other day with an excelent character analysis but no plot. So I feel they both are equLly important in the making of a good book.