Oxygen Not Included is a great game (if you have what it takes to enjoy it).

At first, it could easily be mistaken for your basic colony building game: Manage resources, make your people ("duplicants") happy, feed them and build a base.

The early game is somewhat approachable even though you'll be making mistakes which will only have consequences a few hundred cycles (in-game day/night cycles) later.
Your duplicants will try to kill themselves once you stop watching over them, they will piss in your clean water supply, eat through all of your food and medicines, sneeze, fart and vomit, slowly filling up your base with polluted oxygen and henceforth get sick from it.
The game will throw problems after problems at you, all of which can be fixed using one or many ways.

Then mid game happens and you will begin to realize why so many people find this game overly complicated. The mid game expects you to manage fluids, gases, temperature and so many constants that you will feel overwhelmed and dream of ONI at night (those dreams would more often than not be nightmares actually). By the time you're confident enough with the mid-game (steel, plastic, cooling and atmo suits mostly) you should be about 500 hours in (real-time).

From there, expect to double your play time before you even try to reach late game and space exploration and/or magma/ice management.

By reaching over 1300 hours on this game, I can confidently say that I am somewhat okay with late-game and all that the game can throw at me. I've built hundreds of colony on this game and all of them had their own set of problems to solve. The problem that killed the previous colony is something to learn about for the next one and hopefully this next one will go one step further than the last. Emphasis on "hopefully".

The late game is where the heaviest in game slow-killer makes its entrance: Temperature. Your 900 cycles of a sustainable colony will start to overheat and eventually break and/or melt. None of what you built will work anymore, you'll be pumping 70 degrees Celsius oxygen into your base, burning your crops and turning your water supply to hot steam.

No water equals no oxygen. No oxygen equals death.
The Oxygen is indeed Not Included.

This is one of many ways things can go wrong and trust me when I say that things WILL go wrong. From basic math to advanced chemistry through engineering and thermodynamics, this game has it all.
Expect to spend half of your play time on a debug/sandbox map to test things out, read hundreds of wiki entries, make spreadsheets and watch a lot of YouTube content.
There is no other way around it.

If you want a rather chill colony game, Oni is simply not what you're looking for. If you want to learn and think/solve problems (A LOT) then it's the best of its genre.

Add to that Klei's awesome and unique design, music and overall identity and you've got yourself a game that is indefinitely replayable and enjoyable.

Oxygen Not Included is a great game (if you have what it takes to enjoy it). At first, it could easily be mistaken for your basic colony building game: Manage resources, make your people ("duplicants") happy, feed them and build a base. The early game is somewhat approachable even though you'll be making mistakes which will only have consequences a few hundred cycles (in-game day/night cycles) later. Your duplicants will try to kill themselves once you stop watching over them, they will piss in your clean water supply, eat through all of your food and medicines, sneeze, fart and vomit, slowly filling up your base with polluted oxygen and henceforth get sick from it. The game will throw problems after problems at you, all of which can be fixed using one or many ways. Then mid game happens and you will begin to realize why so many people find this game overly complicated. The mid game expects you to manage fluids, gases, temperature and so many constants that you will feel overwhelmed and dream of ONI at night (those dreams would more often than not be nightmares actually). By the time you're confident enough with the mid-game (steel, plastic, cooling and atmo suits mostly) you should be about 500 hours in (real-time). From there, expect to double your play time before you even try to reach late game and space exploration and/or magma/ice management. By reaching over 1300 hours on this game, I can confidently say that I am somewhat okay with late-game and all that the game can throw at me. I've built hundreds of colony on this game and all of them had their own set of problems to solve. The problem that killed the previous colony is something to learn about for the next one and hopefully this next one will go one step further than the last. Emphasis on "hopefully". The late game is where the heaviest in game slow-killer makes its entrance: Temperature. Your 900 cycles of a sustainable colony will start to overheat and eventually break and/or melt. None of what you built will work anymore, you'll be pumping 70 degrees Celsius oxygen into your base, burning your crops and turning your water supply to hot steam. No water equals no oxygen. No oxygen equals death. The Oxygen is indeed Not Included. This is one of many ways things can go wrong and trust me when I say that things WILL go wrong. From basic math to advanced chemistry through engineering and thermodynamics, this game has it all. Expect to spend half of your play time on a debug/sandbox map to test things out, read hundreds of wiki entries, make spreadsheets and watch a lot of YouTube content. There is no other way around it. If you want a rather chill colony game, Oni is simply not what you're looking for. If you want to learn and think/solve problems (A LOT) then it's the best of its genre. Add to that Klei's awesome and unique design, music and overall identity and you've got yourself a game that is indefinitely replayable and enjoyable.