In this new trailer for Rise of Nightmares SEGA released, we get an idea of what the game is about. Judging by the trailer, it looks like the player is caught in the middle of a madman's ritual in an attempt to raise the dead. Since there are a TON of undead in the trailer, it's assumed he succeeded and you must now fight your way out of this hellish nightmare. In terms of weaponry, the games seems to have the player using a lot of melee weapons as chainsaws, machetes, and knives can be seen sprinkled through the trailer.
You can also expect gallons upon gallons of blood to be spilled during your time with Rise of Nightmares.