The story is this, you are a young child lost in a world of beasts trying to escape. On the way, you find that these beast are friendly and are even kind enough to help you reach your destination. Undertale has a bunch of simple yet charming puzzles that eat up time, but make you smile when you complete them.
The music is beautifully composed and paints the world with detail. It is amazingly beautiful, and makes you question your actions because, in this game, you will be held responsible for all that you do.