Oxygen Not Included

Add it all together and Oxygen Not Included is a singular achievement: a space-colony simulator built on real thermodynamics and fluid physics, wrapped in cartoon charm, and supported for nearly a decade into one of the deepest systems sandboxes ever made. It is Klei's nine-year live-operations benchmark and, for the right player, something close to an engineer's Bible — a game that translates chemistry and physics into play so completely that learning it feels like learning a discipline.

A Benchmark for Systemic Depth

What makes ONI extraordinary is the integrity of its simulation. Nothing is faked; every gas, every degree of heat, every drop of water obeys consistent physical rules, and the entire game emerges from those rules interacting. That foundation gives it a depth of engineering and optimization that almost no other game even attempts, and it is the reason the game rewards mastery so richly — your knowledge transfers, your intuition sharpens, and a base you build at three hundred hours would be unthinkable at thirty. The cartoon shell and the brilliant overlay system then perform the second miracle, making that forbidding simulation legible and even warm, which is how a hardcore physics sandbox ended up with a 96-percent-positive rating across more than a hundred and thirty thousand reviews.

The longevity confirms the achievement. Five DLCs, a vast mod ecosystem, and a 2024 Steam Labor of Love award testify to a game that has not merely survived but deepened across nine years, sustained by a community that treats each new colony as a fresh engineering problem to solve. It is the kind of title that defines what its genre is capable of.

Who Should Buy It

This is for the player who loves systems for their own sake — anyone who finds joy in untangling interlocking mechanics, optimizing a process, and turning chaos into a humming, self-sustaining machine. If the idea of genuinely understanding the Carnot cycle in order to cool your base sounds thrilling rather than exhausting, ONI will give you a sandbox of effectively infinite depth and one of the most satisfying mastery curves in gaming. It is a near-perfect fit for fans of Factorio, RimWorld, and Dwarf Fortress who want the engineering dialed to its physical extreme, and for the curious tinkerer who is willing to learn a hard thing because the reward is so concrete. It rewards patience and intellect more generously than almost any game on the market, and the community around it is one of the most knowledgeable and helpful anywhere, full of veterans who delight in explaining why your base boiled and how to stop it next time.

It is also, unusually, a game that can teach you something real. Many players come away with a working understanding of thermodynamics and fluid mechanics they did not have before, which is a rare and genuine value that few games can claim.

Who Should Skip It, and How to Start

The caveats are blunt and important. Players with no patience for a steep learning curve should know ONI's is among the steepest in gaming, and most newcomers genuinely cannot progress without consulting tutorials and guides — if leaning on outside help to understand a game sounds like a chore, this will frustrate you. Players without any STEM grounding or appetite for physics will hit hard walls in the mid-to-late game, and anyone wanting a relaxing experience, an authored story, or the ability to play on a console or phone should look elsewhere entirely, since ONI is demanding, plot-light, and PC-only. For those undeterred, the path is clear: start with the base game and give yourself permission to fail repeatedly while you learn the fundamentals, lean on community guides without shame, and only add the Spaced Out expansion once you are comfortable, approaching the divisive Bionic Booster Pack with caution. Survive your first sustainable colony, and you will understand why this game inspires the devotion it does — which is exactly the experience this final score is built to honor.