The end of a story is the most important part. The end has to tie everything together and should address the beginning in some way. Most importantly, the end has to evoke an emotional response in the reader. I'm not kidding. The end has to make the reader feel something. Maybe it's only satisfaction that everything was wrapped up or 'Huh, interesting idea,' but it has to be something.
One of my fellow RMFW members wrote a very interesting (long) blog post lately about emotion: Emotional Barrier in Fiction: The Most Important Barrier For You To Cross (Part One). When I wrote the story that was my first pro sale, I was sobbing at the end as my protagonist sacrificed herself for her family. Was sobbing and sale a coincidence? I think not.
The tricky thing about evoking emotion in the reader is you have to make the reader care about the protagonist. I took a creative writing class last Fall and the young students tended to go right for death, dismemberment, rape, etc., before we cared about the characters. The teacher said they didn't "earn" the drama. How do we make the reader care? I think the author has to care.
What do you think?
Good luck with your emotional endings!