You're a man armed only with his grapple. Being chased by lava, water, and other things that can kill you, you need to go up.. and keep going up until you are far away from any danger. Grapple Hero is a different take on the platform jumper games, where your only means of movement is attaching your grapple to the next platform above you.
Going to follow this pattern for the 4 worlds. Beat 6 standard stages and then have some type of boss challenge. The boss challenge could be anything from beating a rising tide of laval, to actually racing another chracter.