A great ending will leave readers feeling satisfied.
While blog hopping I have seen many book bloggers ask the question, 'at what point do you give up reading a book with a weak storyline.' I've been surprised at how many readers plod on to the end because they need to know how the story ends. Most rants on review sites and Goodreads are about weak endings.
My advice? Maintain the tension in the story until the last possible.
Follow Bell's advice for a knockout ending,
'As you near the end, it should look as if the opposition is the one who will win. He has everything going for him. The Lead is up against the ropes. Only when the Lead reaches deep within and makes her move will the knockout blow be thrown.'