Looking sullen means appearing gloomy, sad, and unhappy. Some antonyms for looking sullen include looking cheerful, happy, delighted, and pleased. If someone is not looking sullen, they might be looking contented, joyful, upbeat, or optimistic. An individual who is not looking sullen is displaying a positive outlook on life and exudes radiance and warmth. Some other antonyms for looking sullen could be appearing hopeful, confident, enthusiastic, lively, or enthusiastic. When someone is not looking sullen, they bring a positive energy and can infect others with their cheerful disposition. A non-sullen individual brightens up the atmosphere and brings about a sense of light and warmth.