It depends on the genre of course. For fiction, I love the character development. It's not just a simple stick drawing on paper. Creating an entire character involves so much from names to how this person fits in their world. Think of it as detailed and intricate as the Sistine Chapel.
Then there's making sure that the world you're creating will seem real to the reader. You have to consider families, friends, government if that's necessary, schools, public places, sometimes even if this story takes place on Earth.
Creating all of that is more than plotting and planning. It becomes an adventure all of its own. It's intriguing learning it as you go.