One of the things that I'm learning about revising is that the more times I work through my novel, the more I can enhance the layers and depth in the story.
Sometimes I do this by adding a small detail, such as by a clue to the character's age or family background. Sometimes I rewrite sections of dialogue to bring out more personality in a minor character. As I get near the end, I may even rewrite an entire chapter, making the events in the ending clearer and more dramatic. The scariest part for me is adding entirely new sections, because I always worry that the story will become too long.
It's impossible for me to make everything work in two or three passes through the novel. I think this will be my fourth or fifth time. How many times do you go through your entire novel to revise?