Alexander's works are usually coming-of-age novels in fantasy settings where characters fulfill quests. The main characters are common people who return to their regular life after their quests. While his settings are inspired by fairy tales and legends, his stories are modern. Self-acceptance and awareness are vital for the protagonists to grow. Alexander's works are fundamentally optimistic about human nature, with endings that are hopeful rather than tragic. He stated that in his fantasy world, "good is ultimately stronger than evil" and "courage, justice, love, and mercy actually function." The Prydain Chronicles deal with themes of good and evil and what it means to be a hero. The Westmark Trilogy also explores good and evil and shows how corrupt leadership can lead to unrest and revolution. The main character, Mickle, reluctantly joins the army in an unexpected war, subverting typical war heroics. The books are appealing adventure stories that simultaneously discuss ethical issues, a quality critic Hazel Rochman praised in "School Library Journal". Writing at "The Horn Book", Mary M. Burns stated that "The Illyrian Adventure" was excellent because it was believable while being a fantasy and had a strong underlying theme. Alexander himself remarked that his "own concerns and questions" still came out in his fiction. He consciously used fantasy stories as a way to understand reality.