Should be careful not to just shut down player ideas. If everything they do slams into an annoying problem, it can quickly stop being fun.
I sometimes try to sync with the players and be like “hm do you think the 300 year old vampire has had to engage with the city before? What sort of plans and influence do you think he has?”. Then it doesn’t feel like I’m just screwing them, if they’re thinking about it too.











I’m not sure I follow what you mean by originality and complexity as opposed concepts.
It’s important for players to be able to engage with the content. If you add too much new stuff up front, they’re not likely to retain it. If they can’t retain it, they can’t engage with it. You can drop them in store brand middle earth and they’ll be able to engage. If you drop them in a wholly original setting with winged squid people, eternally young goat poets, and living clothing, that’s a lot to try to integrate all at once.
One of the most disappointing games I ran was Vampire, where the players just didn’t do any reading about the game’s fiction or factions. They didn’t understand what the major NPC players wanted, so they were always lost and confused. After we abandoned that game, I started a new one that was basically Diablo. They did a lot better in that one, in large part because there was no up front details. Yeah yeah fallen kingdom, demon problem, we get it.
I think the real factor is “how much new stuff do they need to learn to engage?”