The world is a bleak and dangerous place, and there's an overarching sense of dread and foreboding. Some of the remaining humans are quick to band together to work toward a common goal: survival. Others exploit and even kill other humans to remain alive.
Characters experience frequent, intense acts of violence involving blood (pooled, splattered, dripping, etc.), shootings, and decomposing, half-eaten bodies. Beloved characters die, and children are threatened, injured, shot, killed. Many tense scenes draw out suspense and fear. Survivors are injured in terrible ways that are shown at length onscreen. Characters are suddenly dispatched onscreen. One season's main villains are cannibals, and body parts are shown, as is a group of people who are kept for food like cattle.
Most episodes contain no sexual content, though there is some flirting, embracing, and caressing between couples. In a handful of episodes couples have sex -- in one episode you can see a man behind a woman in an obviously sexual position and in another episode a woman puts her hand on a man's crotch and they embrace and offscreen sex is implied. In later seasons, male villains rape female captives (offscreen). A few episodes refer to sex, pregnancy, affairs, birth control, etc. Patients at a hospital are forced to submit to sex with officials in order to receive treatment.
Some unbleeped swearing, including "s--t." Other audible words like "pissed," "damn," "bitch," etc.