If I had to pick only one thing, the setting.
It's the culmination of every story, campaign, and adventure my friends and I have been a part of over the years.
The characters would be a close second, as I pour a little bit of myself into each of them.
My hopes. My wishes. My dreams. All to bring them to life on the pages.
Ultimately, though, it isn't about me; but what the readers bring to the stories as well, and how the stories may impact their lives or inspire them in ways we can all hardly begin to imagine. That, in truth, is what I like most about fiction in general.