For a light-hearted game, Oxygen Not Included takes laws of physics and biology very seriously. Characters, or Duplicants, require regular meals and fresh water. They can hold their breath, but only for a limited time. Extremely cold and hot temperatures hurt them. Given high enough stress level, they can even experience nervous breakdown that causes them to vomit excessively or start binge-eating colonie's food supplies.

Every Duplicant has a name and unique appearance, as well as personal traits. They are very cute and funny, which makes you fully invested in their well-being.

This game provides a real challenge when it comes to planning your base's inner layout. You need to take into account gas and fluid dynamics to ensure that your Duplicants have breathable air and aren't intoxicated by contaminated water.