I'm actually really happy with how world building went. I came up with a basic idea: a world where magic and non-humans hadn't existed for thousands of years, but suddenly magic begins to return--kind of like Shadowrun, but without the cyberpunk. Then I added in a group modeled vaguely on the Overseers from Dishonored to be a force of anti-magic social sentiment.

The next step was a couple of prequel oneshots. Since I'm bad at oneshots, those ended up being 4-5 sessions each. They were set about 30 and then about 15 years before the return of magic, and allowed the players to become familiar with the basic setting and to introduce some places and characters.

The crucial step was then doing a few rounds of Microscope with the players. Using that as a worlbuilding tool after we already built a shaded understanding of the basics of the world allowed us to collaboratively generate a really detailed and interesting history.

Between the oneshots and Microscope, the players are all really invested in the world they're playing in. I can throw out references to things and they actually catch them and are excited by them, because they're either things that their oneshot characters did or experienced, or they're things they created themselves in Microscope.

Needless to say this all made for tons of notes in Obsidian.