My setting is based on the 4E implied setting with my own take on things.
1. What is the theme of your setting? (It could be a genre, but it could also be a general vibe or feeling that the setting is themed with.)
2. What is the world like? Is it a continent? A city? A universe? Another dimension? A room? What about it?
3. What are some of the cool things about that world? Their denizens? Their landmarks? Rumors and legends?
4. Perhaps some history on the setting would be in order? Maybe discuss the fate of the setting as well?
1. Not sure. "All you need to get what you want is the will to make it happen" is maybe one. "And in the process you will be changed." Maybe that's another. I haven't really thought about it that much.
In terms of genre, it's weird fantasy. I think I was calling it "post-apocalyptic science-fantasy western" at one point.
The setting is harsh - civilization is dead. Monsters roam the wilderness, the few settlements that survive are small and threatened, and new warlords are trying to fill the power vacuum. Many civilizations have failed; the medieval world is filled with ruined "cities of glass & steel" (modern cities with skyscrapers), strange ziggurats built for human sacrifice, cities of snake-men, devil-worshippers, etc.
A couple of sessions ago a PC got a space ship (think Tintin's rocket ship) so she could travel to see a god on a distant planet (and fought some of his "angels" - androids).
There's occult magic that makes its practitioners "strange" (social outcasts). Cults that serve distant entities who dispense power for a price. Religions created by the "gods" to indoctrinate mortals - as well as teach them how to alter reality as they wish.
2. The setting is a universe - a small one, more like a single solar system. I had the idea that it's a holographic "universe" trapped in the accretion disc of a black hole in our reality. Just because I think it's neat.
3. I try to make sure that there's lots of weird stuff out there. Instead of a dungeon being an abandoned mine it might be an old missile silo or nuclear power plant or factory for processing human sacrifices.
I try to make sure there are lots of opportunities for change - the PC I mentioned with the rocket ship has seen her STR drop to 3 (but she was lucky and grabbed some randomly-generated and placed gauntlets of ogre power), she shares her soul with a dead demi-god (who she "convinced" to die after she altered his world-view), and she just got brain surgery (infected with nano-bots that - luckily, after a passed save - increased her mental abilities), so now her head's shaved and some Matrix-like plugs are jutting out of her skull.
4. The setting is 4E-ish, with primordials and gods and all that, but I've made some changes. I have a timeline that I use when I roll up a magic item - I want to know who created it and why, and that colours its powers. (The ancient dwarves made magic items for different purposes than the more recent dwarves - e.g. "Mixing earth and stone to create something new and unique" vs. "A desire to possess more and more and more".)
The fate of the universe came up in the last game. The PC was talking to a pair of angels of knowledge - she wanted to find out what they truly loved (so that she could get some more power from the dead demi-god with whom she shares her soul - a warlock-patron set-up). They truly loved the acquisition of knowledge, which means learning new things, which means change is necessary; but eventually change will lead to a point where they can't store that knowledge, and that means no more learning is possible (some kind of entropic death of the universe). They could try to stop it but that would mean stopping change and they'd be in the same boat. I believe they called this the "Thardizdun Paradox".
But who knows what's going to happen. The PC in question has (the belief that it is) her destiny to create a new universe. Maybe that will happen. That's why we play.