I would say a large part of Undertale's soundtrack is good, but I actually think the game is not very good.
Heartache - https://youtube.com/watch?v=xflkF-sqNaM
Spear of Justice - https://youtube.com/watch?v=qrBB3_rFPjg
Bonetrousle - https://youtube.com/watch?v=zdeZwAk6ULE