The novel depicts the themes of identity, race, peer pressure, dehumanization, crime, teenaged masculinity, and the relative or subjective nature of the truth. This idea comes up multiple times throughout the novel. There is the truth in relation to the law, but also the truth of a person's character. Steve, during the trial, writes about experiences he has had that directly contradict the thug persona he has been labeled with. The book reads like a formal screenplay, written by Steve Harmon, interspersed with seemingly handwritten fragments from his diary. The screenplay's verisimilitude is enhanced by such cues as "fade in," "voice over," and “fade out." As one critic wrote, the novel is "Presented alternately as the first‑person, handwritten memoir... [and] a neatly typed screenplay." Critics have commented on how the novel offers "surface effects – marginalia, drawing, photographs, mugshots, and video stills – to offer an analysis of the complex identities that emerge in the context of such surfaces." Generally, the novel has been praised for remarkably sophisticated levels of thematic and formal complexity, considering its ostensible status as a young adult novel. As another critic wrote, "Monster is an experiment in form and structure," demonstrating Steve's "vent[ing of] his passionate perplexity."
The novel is interspersed with various photos depicting Steve. Many appear to be placed around the prison, possibly taken after he has been released as he is dressed in plain clothes although his oversized T-shirt is striped. Possibly indicating that he will never be free from this experience. Myers had an affinity for addressing issues of race in many of his other novels as well as several articles he penned.