Undertale is a highly praised story and strategy game. You play as a genderless child who has fallen into a place called The Underground, where the humans banished the monsters. It is a choose your own adventure game as your actions are taken into account throughout the whole game. You are given a choice, to kill anyone who crosses your path, or befriend them. These are called the Genocide and Pacifist route, anyone who does a mix or incomplete version of these rought is on a newtrule rought. Your character is the most important character of this story, because depending on the route you take, you are either the savior of the underground, or the killer of it.
Story and lore are given to you gradually throughout the game. The excuse of puzzles are even enforced sometimes, as there are monsters trying to trap and kill you, since you are a human.
If you go the more popular route of the pacifist route. Your job is to befriend every monster in the underground, no matter how much they try to kill you. Your reward for befriending every single monster, is freedom from the underground, with new family and friends to live on the surface with. This route requires more patience, persistence and care.
The more difficult route is the genocide route. Where your goal is set on killing every last monster in the entire underground, until there is nothing but dust. Your reward for your mass genasis, is the ghost of a former human child who was down here, haunting you and setting out to destroy your world and all others. This route contains much more fighting skill and extreme patience, in order to make sure you have killed everyone.
This bullet hell, choose your own adventure RPG is loved for its story and the connection you gain to the characters within it.