We spend a lot of time talking about story openings. Most of you probably know that if your story has a flat opening, if it doesn't grab an editor's attention right away, you're probably getting a rejection slip. Well, the same thing is true for your ending. In fact, if people hate the way your story ends they're not going to remember your subtle characters, your wonderful dialogue, your deft use of the semi-colon. Instead, the only thing they're going to remember is how disappointed they were by the ending.
This does not mean your story needs a "happily ever after" ending. Sometimes, that's the worst way to end your story. What I mean is that the reader must be satisfied with the ending. You want your reader to walk away from your story thinking, "Yes, this is the way that story was meant to end." Maybe someone dies. Maybe the girl doesn't get the guy. Maybe she does and everyone lives happily ever after. It doesn't matter. What does matter is that the ending fits. That it's satisfying.
Let me give you an example. If you're old enough, you remember the television series M*A*S*H (if you're not old enough--I don't want to hear it)! The final episode of the series, titled, Goodbye, Farewell, and Amen was the most watched television broadcast in history (until the 2010 Superbowl) and for good reason. I'm not going to recap the episode, it would take too much time; however, if you're interested here's a link to a good summary.
I wouldn't classify it as a happily ever after ending. Yes, the war ended and the soldiers/doctors went home; however, they left knowing most of them would never see each other again. In my opinion, the reason the ending works is because the writers stayed true to the characters. The characters grew while remaining true to themselves. It was bittersweet. It did not downplay the horrors of war. It wasn't all "YAY, we get to go home!" It was a whole bundle of human emotion--good and bad, beautiful and ugly. I was in my early (very early) teens when the episode originally aired and I still remember it. That's good writing.
That's what a good ending can do. I've seen plenty of shows end since then, but that final M*A*S*H episode is still the best. As writers, we need to spend as much time crafting the endings to our stories as we spend writing that perfect opening. I've rejected several good, really good, stories simply because the ending fell short. Don't let this happen to you. You deserve more. Your story deserves more.