Let's talk about fairly advanced game design topics for base-building games. Games like Rimworld or Dwarf Fortress or Evil Genius or Minecraft or - in this case - Oxygen Not Included.
Nearly every base-building game has some kind of progression. You start with the lowest-level stuff, and unlock higher-level stuff over the course of the game. For example, you typically unlock better methods of heating and cooling your building, or better crops, or advanced building materials, or all three.
The question is: how do you unlock them?
There are a few basic unlocking methods, and we can show them by example.
You want to build a fridge/food storage room in Oxygen Not Included. At the beginning of the game, there's nothing like that. So what do you do?
1) Research a fridge.
2) Build your fridge room in a part of the map that's cold.
3) Scout around for cold-creating plants and replant them back at your base.
4) Use the physics of gases to create a carbon dioxide trap, which is considered a sterile environment by the game.
5) Evade the question and micromanage your food production/create pickled foods that can be stored on a shelf.
There is no "right" solution: which tactic you'll take will depend on your goals, your resources, and your world map. This makes for a very flexible, deep game, so it's worth examining these in detail.
1) Point-centric solutions involve spending time and resources on generic "points" to unlock a new method. This is almost always a research desk, often one with multiple tiers. For example, a fridge requires a tier 2 research desk in ONI. This is a very typical approach and pushes the player to make a "high functioning" base that has enough spare effort to build up those points. Unfortunately, this can backfire: once a base is high-functioning enough to spend time on research, you will need to introduce new challenges and complexities to keep the player struggling. Typically this is done through ever-increasing supply chain complexity with ever-increasing manpower demands. All told, this approach focuses on building a base that can function smoothly and efficiently.
2) World-centric solutions involve building facilities in parts of the world that fit your needs. This is often a random biome situation, which means that the player will examine the regions around each new base and figure out what biomes can be exploited. In other situations, this might be non-random biomes - for example, if you build mines at a certain depth in Minecraft, you know you'll get slimes. In some cases it's sort of halfway between the two - for example, it's technically random whether you have an aquifer below you in Dwarf Fortress, but you're told up front and it's extremely common. Anyway, world-centric solutions push the player to expand their base and create satellite facilities, and make rapid transit/cargo systems valuable.
3) Scout-centric solutions involve going out into the world in search of small amounts of specific resources. In terms of gameplay pressures, this is similar to a points-centric approach: is your base running efficiently enough to send people away? A few notable differences: points-centric is predictable and not random at all. Preparing resources for those that will go scouting is often more expensive than feeding the researchers. Monitoring the explorers and clearing their path eats more player attention than letting researchers research. Also, the resources found in the world are typically limited but cheap to deploy, unlike the unlimited but expensive unlocks from a research base. Having both a scout- and points-centric solution to core problems means players can weigh a variety of tradeoffs and make a choice unique to their current base instead of always having a best solution.
4) Physics-centric solutions involve constructing things such that the base generates a solution based on its layout. For example, in ONI, carbon dioxide sinks below oxygen. It's relatively easy to create a carbon dioxide trap by simply laying your base out properly. This is more commonly seen in "dungeon-builder" games, where various monsters can cause various effects and you can level them up or get better monsters based on what neighbors they have. These are typically "high skill" solutions, but it's risky: be careful not to allow them to become the dominant strategy, or advanced players will not need to take any other approaches.
5) Evasion solutions allow the player to simply not take that path by having a build that doesn't require it. You can play almost any base-building game without a fridge if you orient your food chain around not needing one. This allows players to develop radically different kinds of bases, and is a highly recommended option to include.
These five approaches, used in tandem, allow for amazingly deep gameplay that never repeats. When I saw the tech tree in ONI was so sparse, I got a little annoyed... until I realized how diverse the alternate approaches were. I don't think ONI's balance is quite right, but the ideas are all there: competing methods to get the same result, meaning each base has new and unique tradeoffs.
This is especially critical when there are timers involved. If you have infinite time, a sub-par approach will just take a little longer. The timers are necessary to produce stresses, although obviously it's best if they can be tweaked for different kinds of players.
As an example of where I don't think ONI does it quite as well, let's talk about the most brutal timer I've seen in a while: the oxygen in Oxygen Not Included.
Your people breath a lot of oxygen. Huge amounts. The main method of creating oxygen involves burning algae, a substance which seems common when you get started... but as your rate of consumption increases, you'll suddenly find you've run out. This scales with the number of people in your base, obviously, which means as your base expands oxygen becomes more of a pressure.
1) Technology. Since this highlights a smoothly-functioning base, you'd expect this to be a "set up oxygen with your algae, then research a replacement while you can still run smoothly". However, the technological solutions are pretty rough. One involves inefficiently burning a rare resource (slime) to get algae. Another involves burning a limited resource (water) to directly get oxygen. Another involves generating large amounts of poison oxygen, then converting it into regular oxygen. These are all a bit complex and wonky, but that's part of the fun.
2) World-centric: there are slime/algae-rich biomes. Most bases start with one nearby. However, there is no biome which actually generates algae or oxygen, so those locations will get mined out. Technology levels unlock more options, but they feel anemic. There are areas of the map which have oxygen in them, but none have enough oxygen to matter. There are special stones which emit oxygen, but it seems they are never fully contained, so within a few days they have all burned out everywhere in the world.
3) Scout-centric: about the only oxygen-related things you can scout for are slime puffers. These (slowly) cycle poison into slime. Normally, that slime re-emits the poison, forming a permanent cycle. You can painstakingly herd them into farms and use alternate poison sources to create slime, but herding them is extremely laborious and each one doesn't even seem to support a single person's breath after all the conversions are factored in.
4) Physics-centric: because your team can hold their breath and will walk to where there is oxygen to breath, it is possible to save on oxygen generation by only filling the top layer of your base with oxygen, reducing the loss of oxygen through secondary costs such as being absorbed into rock or lost through an airlock. This is, however, marginal. I would love to have a physics-based solution for creating algae, or even directly creating oxygen.
5) Avoiding it: your crew can breath poison, at least in this update. They really don't like to, but they can. Poison sources are extremely easy to find, to the point where avoiding them is a big part of the game. Instead, embrace the filth and you don't even have to worry about it.
I hesitate to offer "solutions" to what I consider to be a weak game element. After all, this weak game element is the core timer for the entire game, and there are a number of interesting routes you can take... it may be that small balance tweaks would be enough to satisfy me. But with that said, let's talk about how I might have chosen to set this challenge up.
In my magical imaginary version of ONI.
1) At higher tech levels, I think we would be able to exchange time, space, work, and condition management to create an alternate algae or oxygen source. For example, what about an "algae box"? Needs irrigation, a dense carbon dioxide atmosphere, and a high temperature. With effort, you can now grow algae - but it takes carefully building your base to do so. How about an even more advanced science for creating oxylite out of massive quantities of hydrogen or natural gas or something?
2) World-centric. I would like a biome that generates oxygen, water, algae, or slime in quantities high enough to live off of. Right now we do have steam geysers, and water can be turned into oxygen, but it requires very advanced tech. We also have slime biomes, but they don't produce slime. Puffers live in them, which can give the illusion of slime production, but no slime is actually being created. Perhaps a coral biome which slowly emits oxygen? Cutting the coral destroys the oxygen-emitting elements, so you just have to live there, or perhaps create a long gas pump.
3) Scout-centric. I like the puffers. I want to be able to tie a rope to them, or maybe stuff them in a sack, so they can be moved into farms more easily. I also think the puffer's rate of poison-eating should depend on the density of the poison in a very big way - if I can get them into dense clouds of poison, I want one puffer to support at least three people's breaths.
4) Physics-centric. I would like physics methods for creating slime, algae, or oxygen. Perhaps something like "boil poison water to get slime" or "pure water flowing through dense natural gas turns into algae" or "plants turn carbon dioxide into oxygen". Not sure why that last one isn't a thing.
5) Avoiding it. Right now the only method for avoiding oxygen consumption is to breathe poison. I can think of three other ideas. A) Make building a base with a low headcount viable. B) Oxygen booths which don't emit oxygen, but can be visited when you need a breath. C) Breathing poison or some not-quite-oxygen mix simply causes their learning to shut off - no skill growth, no research, maybe a stat penalty.
In the end, I like ONI.
I don't think they used this "five approaches" technique on purpose, but it's worth thinking about the best base-building games you've played, and what you enjoyed about them. It's certainly worth expanding the options within your own base-building games: the cost is typically much lower than you think.
Anyway, those are my thoughts. What are yours?