Rain World is a sidescrolling platformer in which you play a small rodent who must survive on a planet of other life forms pelted with recurring lethally powerful downpours of rain. You must learn to control your creature (who moves with dynamic physics, along with all other creatures), and learn to interact with and hunt the various other creatures (who have varied and intelligent AI and are not necessarily hostile) in order to gain food to sustain you through the next rain cycle.

Through all of this you explore a large interconnected world of different areas that show a background lore of a world that previously inhabited intelligent industrial beings (who have vanished) and uncover the mysteries within and find others of your kind.

That was as succint as I could make it to show off the unique qualities of Rain World. Its visual style is beautiful, its gameplay has a moderate learning curve due to the physics, and the AI of the creatures are successful in creating a dynamic ecosystem wherein the player feels like they're a small incidental piece of a world that has its own goals and behaviors that the player must learn to fit in with and work within.