It's hard for me to try to introduce Undertale without thinking of all the "you may have heard..." jokes back when Michael Jackson died.
It's doubly hard because I know the tendency of the fans (after only a month) to cry "spoiler!" at almost anything.
So... briefly held the top spot on Metacritic.  Now holds a measly 94%, the same as such pitiful titles as Command and Conquer and Skyrim.  You are a genderless human child in a world of monsters, and your goal is not to kill anyone.  There is a talking flower.  Made by the chief music guy from Homestuck.  And that's all I have to say about that.