I have an extensive sci-fi setting built up around my character, as I'm currently trying to write a novel with him as one of the main characters.
It has a commonwealth of many worlds and species that was devastated in a war against an Empire. The setting has a lot of aspects to it, many of which I'm still exploring. It's quite a high-tech setting, which also has some magical elements blended into the technology. It's inspired and has shout-outs to a lot of other things within it, but I'm trying to keep it it's own thing as well.
Prior to the war, things were pretty utopian; there were some bad elements of course since it's a society of many cultures and people so crimes and such still happened, but overall it was a good place.
After 'the fall', things have got a bit tougher, as much of the infrastructure and government has been devastated, and it's slowly rebuilding in new ways. It could go a lot of ways, and there are a lot of aspects to it - there's dangerous places, but there are also good and caring people and places too.