FANTASTIC!
Last session was the first session: Session 0 of my new homebrew campaign. And I explicitly left lots of plot details that weren't of immediate/obvious importance in the first act as undefined to flesh out with the players. This is part of what I wrote:
"I'm going to be putting background details about your characters in your hands as much as you are comfortable.
For example, I have no pre-determined pantheon, so if you want to play a worshiper (cleric or otherwise), we can flesh out who you worship together. Want a compassionate god of the dead? Check. Unsure if you want a kind goddess of hearth, home and community or a strict taskmaster of civilization as your nemesis? We'll talk it out. Is the moon a comforting symbol of womenhood or the ever-watching eye of the shadowy god of secrets?
And this goes for more than that. Want a knightly order, a hermit mentor, a wizard academy, or a thievely guildmaster of street urchins right out of Dickens? We can work it out. "
So after the standard Session 0 stuff we start talking about characters. One person is planning on playing a halfling druid. And be busts out with:
"In some editions, druid worship nature gods, in others just a nebulous 'nature' - where do they get the power? You talk about the moon got me thinking. What if the moon is the skull of a decapitated god. And the continents are just parts of it's mangled body floating in the seas."
We had a lot going on, including people hitting on big things that would impact some of the stuff I'd written - but would work in very nicely, perhaps better than what I originally had.
In the end, everyone left inspired and with details of their character to work out, and I stayed up until Dark O'Clock in the morning writing up notes from the session so I don't drop any.
All in all a very successful session 0, and bodes well for the first play session of the campaign.