Nier went through the inspective lens of the ESRB and they came back with an amusing and somewhat informative summary.
The game has some puzzles, “shooter”-style mechanics, and apparently Nier gets to ride a boat. Read the full description to see what other swear words Kaine uses to spice up cutscenes.
In this action role-playing game, players scour a post-apocalyptic world for a cure, something to save a young girl from a mysterious, magical disease. Players assume the role of the girl’s father and do their best to solve puzzles, travel fleet of foot (sometimes by boat), and perform a variety of quests (fetching items, finding characters, making deliveries, etc.). They also kill an assortment of otherwordly creatures along the way.
Players cast their magic and hack-and-slash with swords to defeat fantastical foes strewn on open landscapes, lurking in dungeon spaces and cobblestone outskirts. A combo meter tracks the consecutive melee attacks; varying overhead perspectives resemble "shooter"-style mechanics, particularly during the protracted boss battles where giant demon-like creatures explode and scream and bleed. Cinematic cutscenes may also depict humans and creatures getting stabbed, impaled, crushed, or destroyed. But while the melee combat is fast and frenetic, it is often inflicted against the mythical—robots, skeletons, scorpions, and golems, giant eyeballs and glowing shadows.
The dense fountain-like cascades of blood (along with the language) factor highly into the Mature rating: blood will spray, cascading and arching—sometimes in slow-motion—across the battlefield when creatures are attacked; blood also stains the ground, covers characters (one in a white dress), fills up a sink, spurts. The aforementioned language is strong, often employed for comedic effect rather than profane slur: "f**ks, "a*sholes," "bullsh*ts," and "sh*t hogs" (a comrade questions the validity of the word) get sprinkled in the dialogue. And throughout the quest, a hermaphrodite character (female traits emphasized) wears a revealing outfit that exposes most of the buttocks, in most of his/her scenes; depictions of jiggling breasts and deep cleavage are applied to various female characters as well.
Source: Siliconera
I thought it was meant to be summary, the first line could have done fine. I can understand the last part being lengthy because they rate games so they need to have detail of the reasoning behind a rating but the two paragraphs above it are pointless. 
