Let's talk about unscripted, intense moments in a game.
Something that happens organically, as you play.
A lot of games are good at this, and it's the reason why roguelikes are still so popular. It's why Kerbal and Space Engineers have such a long-lasting following as well.
There's an adage: "failing is fun". These games rely on trying, failing, and trying again as a tight iteration loop.
I think this mixes two things. There's the tight iteration loop you get from failing and trying again, but there's also the fascinating and fun loop where you struggle to work through the realities of a situation not going quite according to plan. AKA, "plans-awry" play.
I don't think plans-awry play needs to fail in order to be fun. Struggling and succeeding is often more powerful, because it means your efforts were good enough.
For example, these days I build my Kerbal Space Program landers to survive hard landings. Those would have been failures when I was starting out, but now my landers survive because my planning has improved. That's a potent feeling: "uh oh oh noooo- whew, good thing I planned for that possibility."
I turned a failure into a success.
Fundamentally, this is about a learning curve. A player steadily plans better, sets things up better.
The "failing is fun" theory arises from a learning cliff that the devs sprinkle with glitter. It seems to me that self-directed missions can offer lower bars for success and turn this cliff into a slope. Allowing for smaller final goals, and allowing them to degrade gracefully can make failures into at least partial successes.
Thinking a while, I came up with seven factors I think turn learning cliffs into learning curves. Seven factors that make plans-awry play work.
1) Design refinement/mission arrangement. You need to be able to choose a mission and prepare for any mission you feel like doing in enough detail that you'd prepare differently for the same mission once you know more. For example, choosing different loadouts in Kerbal depending on your comfort in getting to orbit and landing on the moon efficiently.
2) Skill play. As the game unfolds, use your steadily improving skills to navigate challenges to your plan. This might be better ship handling in Kerbal, or knowing how to identify potions in Rogue, etc.
3) World state recognition. As your vision expands, you learn to plan further ahead and understand the world state at greater ranges. For example, orbital exchange windows in Kerbal, or understanding how long you have until a boss fight in the Binding of Isaac.
4) Composite/recursive planning. Allow the player to challenge themselves by trying several missions at once, or help themselves by planning a support mission ahead of time. This allows a player to adjust their plans to serve their skills: if they feel like visiting every Juul moon in one go, they can do that. If they aren't that good at fuel planning, let them send a tanker to Juul first to make it easier. Their choice.
5) Exploits/cheats. In single-player games (or friendly multiplayer), exploits and cheats are a core part of the fun. Exploits and cheats frequently turn into fun high-level challenges and opportunities. For example, the understanding that a torch holds up sand in Minecraft: torches can be washed away by water. Water can be blocked with sand. This is a basic setup which allows people to build a switch! Before redstone, it was the only way to build mechanisms, and even now, it's still used.
6) Cool factor. Allow players to do things that are cool because they are cool. Not everything has to be driven by mechanics. To this end, make missions much more open-ended than you ever expected, especially the low-level missions. For example, in Kerbal the lowest-level mission is theoretically "reach space", but it's so unenforced that people happily build slingshots and see how far they can fling Kerbals. Having a soft, unenforced fail state is a powerful tool.
7) Share-ability. Make it easy for players to share with each other. This partly includes things like screenshots and video: make it easy for players to take good-looking footage. But it also includes things like resharing blueprints, packaging up mod lists so everyone can import things without struggle, and very easy imports of levels, challenges, etc. Perhaps even automatic content sharing within some parameters.
These seven things seem to be really good at giving the player something easy to nibble on at the beginning, when they barely understand anything... and then letting the player just stretch their legs forever as they get more and more skilled. 7) is questionable, I suppose, but I definitely argue that it's part of the same concern.
Now, this isn't just theory for theory's sake.
I'm making a game. How does The Galactic Line do these things?
1) Design refinement. This is probably the most challenging for any game, because you have to come up with gameplay that makes refining your designs deep enough to carry the whole game, but easy enough that a newbie can approach it.
For TGL, I plan to do this by focusing mostly on the crew. A newbie understands the idea of putting people on a ship, they can focus on who they want to put on. They'll just choose whichever stock ship they like best.
This will naturally lead to them understanding how the crews and ships work, as they watch their story unfold. Critically, complete failure is unlikely. While chunks of ship get shut down and people start tearing their hair out, the stock ships will be well-designed enough to limp home even after a disastrous starting mission.
They'll hopefully feel the natural impulse to make their own ships, try longer missions, larger crews, etc.
2) Skill play. In TGL, the skill is mostly about optimizing for longevity by arranging the crew and ship modules. For example, when someone stresses out and something on the ship breaks, you have three options: leave it busted, repair it by salvaging another ship module, or dedicate crewmembers to massaging it into function 24/7. These options are about resource management and planning ahead.
If you do them well, you'll have "slack". You can use this to optimize hobby rooms and relationships, arrange for experience gains or career advancement, or optimizing ship modules for better performance in the next zone. This combined with the use of "redshirt" crew members gives players a lot of ways to manage things live in a skilled or unskilled way.
3&4) World state recognition/composite missions. The player will be faced with a lot of options as to what they want to do, but the most obvious pressure will be from "bounty" missions where people request specific resources from specific places. For example, "get me 30 points of astrophysics data from Beta Sirius". Those will be calibrated for the capabilities of the ship, but there's nothing stopping you from randomly gathering as much data as you want. It has some value.
Understanding how long those missions will take and what resources they'll require can allow you to do several missions at once, either in serial or parallel. If someone wants data from Beta Sirius and another person needs you to pick up five passengers from Gamma Draconis, maybe you can do them both in one run. If things go well.
4) Recursive missions. The game encourages the player to meddle with the affairs of non-space-ship folk using a simple colonization system. Hopefully this will not only allow the players to push through map choke points/extend missions, but also feel invested in the universe they're building.
5) Exploits and cheats. Not sure about this quite yet, but the plan is to make the game moddable and I'm not aiming to prevent them.
6) Cool factor. In addition to trying to let space ships look cool, a lot of the fun stuff is going to come from the way you can make custom crewmembers. As The Sims has shown, there is an impressive appetite for putting all sorts of random people in the stew-pot in different combinations. Want a ship crewed by your favorite band? Your friends? Vampires?
From the other side, colonies can also be made cool. Want to terraform a planet? Want to cover a moon in a huge city? Want to start from just one starving industrial colony on a barren world?
7) Share-ability. This one't a bit tough because it doesn't actually exist yet. The big challenge is that I'd need some kind of central database. Once I have that, automatically downloading ships, mods, stars, and world states is fairly straightforward. It's intended to be a "massively single-player" game.
In terms of making it fun to record/screenshot... I have to think about that some more.
At the end of the day, the plan for The Galactic Line is to focus on plans-awry play with a minimum of actual failing. We'll see how that theory works out in practice.
Anyway, those are my thoughts.