The Entertainment Software Rating Board (ESRB) has rated Metal Gear Solid V: Ground Zeroes, providing it with a mature rating. They also detailed some of the contents (beware of spoilers).
This is the full description provided by the ESRB:
“Content Descriptors: Blood and Gore, Intense Violence, Sexual Violence, Strong Language
Rating Summary: This is an action game in which players assume the role of an elite soldier through military missions in Cuba. Players infiltrate various bases and use pistols, machine guns, and rocket launchers to kill enemy soldiers. Firefights are highlighted by realistic gunfire, slow-motion effects, and large blood-splatter effects. Players can also employ stealth attacks (e.g., choking, knife stabbing from behind) and have the ability kill non-adversary characters/prisoners. One cutscene includes a depiction of blood and gore (e.g., a character’s intestines exposed during a dramatic procedure to remove an object). The game includes an audio file in which a female character is sexually assaulted by male characters; while there is no visual depiction, sounds of ripped clothing and struggle can be heard. The words “f**k” and “sh*t” are heard in the dialogue.”
Some of the stuff described we’ve already seen in the trailer, but especially the last piece of information seems to be new. In any case, Ground Zeroes won’t be a lighthearted game, as we already knew, and this rating seems to back that up.