To the surprise of nobody, I read a lot of articles about the nature of narrative and story in games. There's a lot of perspectives - the idea that narrative is core to immersion, or perhaps it is something that is built post-hoc and retroactively makes the game seem interesting or whatever. People also endlessly argue over when the term "narrative" applies, as opposed to "story" or "plot".
Let me fog up the air even more by discussing "immediate post-hoc impulses". (IPHI)
So, you're playing Saints Row. You see a crazy pink van. What do you do?
Some people won't care. The pink van doesn't perform any better than any other van, and you can always paint a normal van pink in the customization screen.
But some people feel the impulse to steal the van. It's just an impulse: "Oh, interesting! Let's go see what's up!" What they do with it afterwards is not important right now. It's that initial impulse.
How interesting is a particular part of the game? It's a judgment you make very shortly after seeing the particular part of the game.
Can you try to make your game have interesting tidbits that draw the player in like that? Sure. It's especially important in open-world games, where you need the world to be interesting on its own.
IPHI: you see something unusual, you want to investigate. That's the first, most basic level.
However, if you've ever watched people playing a game like Saints Row cooperatively, you've definitely seen them egg each other on. "Oh, a pink van." "DOOD, steal it!" "Hey, it's a piece of crap!" "Drive it into the hotel, man, there's a jump..."
What I'm saying is that there is a fundamental difference in how multiplayer games are perceived by the players, and it has nothing to do with the game.
One player perceives an interesting thing and interacts with it. But he cannot chain into the next interesting thing, because he has to stop and search his environment for it. Not necessarily consciously - but he has to stop paying attention to his current interesting thing in order to pay attention to the world enough to find the next interesting thing, and there's a gap while that all processes.
If there's a second player, while the first player is interacting with interesting thing A, the second player is processing what else is interesting. He can present a ready-made package. He can say, "hey, player one, this is a cool thing over here!" and player one can drive cool thing A over to cool thing B and chain them together. This leads to a man with a shark on his head surfing a pink van while it launches off the top of a car park into the tenth floor window of a hotel honeymoon suite.
Each player can latch onto the suggestions of the others, thinking "oh, he's already seen it and processed it, I'll just take his labels and thoughts." No gap in the experience where you have to stop and look around and think.
This is a fundamentally different experience for both players.
At its heart, you can say that this is similar to the role of a plot or in-game story progression. It presents you with the next interesting thing. But the in-game story is really pretty bad at it. It's good at other things - sense of scale, of emotional depth, creating emotional investment in new characters, and so on. But for being interesting and entertaining, another player who keeps bantering with you is heads and shoulders better.
Obviously, this has methods where it works better or worse. For example, six players is not better than two players. The pacing generally gets too rocky, as player 1 can't participate in five interesting things at the same time, especially when some of the players are halfway across the map.
Also, players are not all equal at this skill. Some players are poor at judging random pieces of a chaotic environment as "interesting" (I am not very good at it). Others are too aggressive about spreading their judgements around ("HEY GUYS COME LOOK AT THIS HEY COME ON THIS OVER HERE COME ON"). Some discard interesting things too fast for the other player to chain into it. Some can't keep track of the other players very well and therefore provide poorly chosen content for this moment in time.
That said, this is a powerful mechanic that doesn't get discussed much.
The next level in the discussion is also fun:
Can you put an NPC into the game which does the same thing?