The ESRB has rated Dark Souls 3 recently giving us more details about the content that will be in the full game.
Dark Souls 3 received a M rating which is recommended for mature players over the age of 17. The game only has Blood and Violence as its content descriptors.
The rating summary posted more details: This is an action/role-playing game in which players assume the role of an undead character trying to rise through the ranks in the ancient land of Lothric. Players use swords, clubs, lances, and magic arrows to kill creatures (e.g., skeletons, demons, ghouls, zombies) in melee-style and ranged combat.
Battles are highlighted by slashing sounds, cries of pain, and large splashes of blood. Some scenes depict characters impaled on swords or lying in large pools of blood. Players can also attack and kill non-combatant characters without penalty. Boss battles depict more prolonged combat, often with large-scale enemies.
From the description above, the game sounds like it will offer a lot of the same things as the other two titles in the series. You are pretty much just a random character that is going around killing lots of enemies including huge bosses.