(cache)Factorio / YMMV

Accidental Aesop: The game doesn't obviously push a Green Aesop, but the player will end up heeding one.
- Pollution is the primary factor that cause the biters to grow stronger, more numerous, and to attack your base, so pursuing aggressive growth of your factory can easily result in you struggling to defend it, and will make expansion more difficult since the biters will be hardier. While trees can absorb pollution, they can only absorb so much and if the area is over-polluted the trees will die off, and this also means that reckless deforestation will heighten your pollution problem. Unless you plan to go scorched earth on the biters, the long-term solution is to learn to live in harmony with them; avoid over-expanding until you can defend yourself properly, and leave forests alone to provide a "buffer" between you and the biters where the pollution your factory generates won't bother them.
- While nuclear power is the best power source in terms of pure energy generation, the fluid mechanics needed to power enough reactors to run a megabase can heavily tax your computer. This is why solar power is the preferred power source for many players, because even massive fields of solar panels put less strain on your computer than a basic inserter. Further, you won't ever need to find new fuel sources for them like with nuclear or steam, they produce no pollution, and their only drawback (no production at night) is solved with capacitors.
Alternate Character Interpretation: It's possible to view the player character as a Villain Protagonist. Sure, you crash-landed on this alien world and are trying to survive, but only a few hours into the game, "survival" can give way to "conquest" as you go on the offensive against the biter nests and exterminate them to secure new resource nodes and more land to keep upgrading and expanding your factory. By the end game, where you can command a massive factory defended by artillery cannons that is producing robotic assistants, Spidertrons, and nuclear warheads, all created by strip-mining the planet's natural resources, you've basically become an technological Evil Overlord.
Difficulty Spike:
- Prior to version 0.15.0, the jump between tier 2 science packs and tier 3 was huge, effectively requiring you to double the size of your factory to automate it. Version 0.15 changed to 5 tiers, with gradual increases in complexity for each type.
- Transitioning to Chemical (blue) and Production (purple) Science Packs are each their own kind of spike.
  - Chemical Science Packs require Sulfur and Advanced (Red) Circuits which require Plastic, thus the player has to initiate Oil production, which is quite complicated, especially for newer players unfamiliar with how the game handles fluids and pipes. Additionally, it's unlikely there's a large source of crude Oil near your starting position, and your starting ore patches are probably running low on resources now, which means it's time to add a train network and start mining outlying patches. This means you need to do a significant amount of expansion into unfamiliar mechanics in order to handle steady production of Chemical Science Packs.
  - Production Science Packs each require an Electric Furnace, a Productivity Module, and 30 Rails. This means your production of everything used to make these items needs to increase substantially, and that works out to pretty much every resource — iron, copper, stone, and oil — needs to be ramped up. In fact, Production Science Packs need at least double the raw materials to make as Chemical Science Packs do. While you could get by with basic crude oil to Petroleum Gas processes for Chemical Science Packs, the amount of oil products needed for Production Science Packs mean you'll have to move on to Advanced Oil Production, which is way more complicated with its different fuel ratios and figuring out how to manage the three types of output being produced to avoid your refineries getting backed up and everything grinding to a halt.
Game-Breaker:
- Modules make the mid- and late-game a lot less taxing on your resources. Speed improves the rate you process materials, Efficiency reduces power draw, and Productivity gives extra output every so often. The impact of Productivity in particular is so strong that they actually nerfed it to only be useable with intermediate products to prevent you getting, say, "free" roboports once every so often, or even extra U-235 and U-238 via Kovarex enrichment processing.^note However, starting with version 0.17.0, the Kovarex process is once again compatible with Productivity Modules.
  - This is made even more pronounced in mods. For example, Bob's Mods adds combined-effect Modules that give you all the benefits of the modules without their normal balancing drawbacks: Raw Speed doesn't cause power consumption to go up, Green Modules reduce both power consumption and pollution production, and Raw Productivity increases Productivity without reducing crafting speed or increased power consumption. Finally, God Modules, which can be disabled in the mod's configuration settings, grant every single Module boost in a single module slot.
- Logistic Bots, once you have the infrastructure and power grid to support them, completely shatter the difficulty of designing your facilities. Plop provider chests at the end of dead-end conveyors and watch your robots automatically take resources that would be left laying around and distribute them to places that need them, and build requester chests in far-off corners of the factory to get resources out there without having to run a long conveyor belt. It's possible to run your entire factory without conveyors or pipes, just let the Logistic Bots transport everything to where it needs to go.
  - There are mods that add Nuclear Bots, which never need to stop to recharge at your roboports and thus further reduce the strain on your power facilities, although they do require nuclear fuel to produce and explode if destroyed.
- The Tank completely shatters the danger of the alien hordes and can kill them without much trouble until the endgame when the highest-level biters show up. Its cannon blasts are enough to kill nests and severely damage enemies, it comes with a submachine gun for general purpose combat, and it has a flamethrower for hordes of biters that close in on you. It also has a massive health pool and can kill enemies by running over them and barely slow down for it, so you can just drive it through clusters of low-level biters and crush them without even using ammo. Its only downside is slow acceleration, speed, and handling, but using solid fuel or rocket fuel helps patch those problems up.
- Laser defense modules. They automatically attack nearby enemies, they stack, and they remain functional when within a vehicle. With a fusion reactor to support them, you can fill your armor with laser defense modules and let your auto-attacks wipe out masses of enemies in seconds without you having to waste any ammunition. Spidertrons can have their own set of laser defense modules, allowing you to hop in and ride it past biter nests Beam Spamming everything to death. And since you can upgrade laser weapon damage indefinitely in the endgame, you'll reach the point where you can remotely send Spidertrons out and they will single-handedly clear out even the largest biter nests in seconds.
- In the endgame, mining productivity research. While it takes time to get it to this point, with enough levels into it your mining machines will produce bonus resources faster than they mine them, and at no drawback or penalty, either. Into the extreme lategame when you're operating a megabase, mining productivity makes the very concept of expanding obsolete; your machines will be producing bonus resources so fast that you functionally have infinite resources, because the ore patches under the machines will take an absurdly long time to run out.
Good Bad Bugs:
- FFF 285 has the developers talk about some minor graphical bugs that were spotted and then quickly fixed during the early phases of version 0.17 testing and development. Of all the graphical glitches shown, the playerbase liked the "biter blood-stained grass" effect the most.
Memetic Mutation:
- Spaghetti Conveyor Belts ^explanation
- “The factory is expanding to meet the needs of the expanding factory.” ^explanation
- The Factory must grow ^explanation
Moment of Awesome:
- When the rocket silo finally opens up after inputting enormous amounts of resources to build the rocket is a ridiculously satisfying moment, especially on the first playthrough. Seeing the silo open up, setting off a Red Alert siren and having it reveal the fruits of your labour is incredible.
- When playing with the Biter difficulty turned up and having to deal with Death World levels of wildlife attacks, it can be immensely gratifying to finally get your weapons and defenses strong enough to not only halt attacks on your growing factory, but drive them back to reclaim land that was being overrun by budget Zerg. Extra points if you drive them back with careful use of the Rocket Launcher with an Atomic payload.
Slow-Paced Beginning: When you start the game you have only one mining machine, you can't build assembly machines yet, and all your tech will be burner devices that need refueling and aren't very efficient. The first hour or two will be spent mining resources by hand, running around keeping your burner devices supplied, and chopping down trees to clear room to build. As you expand your mining, stockpile resources, and build labs and get them researching, you'll be able to start mass production and can begin building an actual factory. Unsurprisingly, mods that provide the player with a bunch of tier 1 gear to skip the tedious burner phase tend to be pretty popular.
Squick: The Spidertron has one of the most realistic spider leg movement patterns ever seen in a video game, making it quite uncomfortable to watch for anyone with even a slight dislike of spiders, and turning it into pure Nightmare Fuel for arachnophobes. The only way to avoid this is to never build Spidertrons, which in itself sucks due to how powerful and versatile the things are.
Tier-Induced Scrappy: Efficiency modules. Broadly speaking, it's preferable to use Speed and Productivity modules to improve your factory's output, and the negative effects of this (increased power consumption and pollution) can be solved by just expanding your power supply and reinforcing your defenses. While Efficiency modules aren't entirely useless, they're mostly used in the early game before the player can defend their base properly, and then later for mining machines (which will probably be on the outskirts of your base and thus more likely to be attacked) and production malls (where crafting speed isn't a priority). Even then however, players will likely stick to the Tier 1 modules, because producing Tier 2 and especially Tier 3 modules takes too many Processuing Units/Blue Circuits, and it isn't worth it for the relatively minor increase in power savings that the higher tier modules offer.
Unwinnable by Insanity: If the map is of limited size, the total amount of ore is limited, making it possible to exhaust it completely before launching the rocket and making the map unwinnable. However, one has to deliberately try to do that by some combination of lowering the resource amount, deliberately wasting resources or turning on expensive and/or marathon mode. Later versions of the game allow for a functionally infinite map size, however, with resource deposits becoming richer and richer as you expand outwards.

YMMV / Factorio