For me it is recognising people across different topics. Somebody who gave useful game advice turns out to paint tiny monsters or have strong opinions about bread. It feels less like a queue of questions and more like a place.
I also like threads that get an ending. If somebody asks for help, I want to know whether they solved it. If somebody starts a project, the slightly messy progress update is often more interesting than the polished first post.
What brings you back when you do not have a specific question?