What is the author's style in Oliver Twist by Charles Dickens?

Dickens uses "flat" characters; his people don't tend to grow or change over the course of the book. Oliver, who begins good, stays good, and he never wises up; never once does he show any awareness that the thieves are truly evil or any real disgust at Fagin's life. He is afraid of the thieves, but he is afraid because they may hurt him, not because he is aware that they're twisted and corrupted souls. Fagin, who begins evil, stays that way. Many of the characters are easily marked by certain "tags" of behavior or voice: Mr. Grimwig habitually thumps his cane on the ground and asserts, "I'll eat my head!"; Fagin is always out for money; Mr. Brownlow is steadfastly good; Monks is obsessively evil. Mr. Bumble is consistently pompous and shallow, and Noah Claypole remains a coward and a bully throughout the book.

In modern fiction, characters like these are considered a mark of poor writing, but in Dickens's time, readers were not bothered by such flat depictions. In addition, because the novel was written as a serial that required readers to remember all the characters for a long period of time, it was necessary for writers to make their characters easy to remember and categorize.