House of Many Things

Mystery and problem solving are essential components to any RPG  of course but the context of any adventure does need to be painted in. There are a number of huge off the shelf universes that do the donkey work for you such as Tolkien, Warhammer, Star Trek etc where the GM instantly has reference material for the world which fleshes down to the minutest detail.

And detail is everything. A bit like a portrait, one simply cant ignore the background arbitrarily; its there for immersion and helps bring a world alive in a quality setting. This starts to become challenging for more thinly written systems or publishers that have focused too much on mechanics and GMs  need to deploy some tools. Typically for myself, societal power structures, factions if you will, provide a wonderful opportunity from the big movers at the top with all the tension you need for a scenario right down to the actions of optionally radical individuals. This was one of the misunderstandings of Planescape which was criticised for being too thin on content. But this was never the intention as its depth is drawn from over a dozen ancient and competing groups, some opaque even to their own followers.

Pushing the boat out even further, there is the option to explore impossible regimes such as Mageocracies (see Wizards of Thay), Necrocracies or of course collectives such as Mindflayers or the Borg. I suspect there is a system somewhere that has combined them all...