Mickey Spillane always worked on the ending of his novels before even starting the beginning. His reasoning was that the ending should always kick ass making both the beginning and middle of the story worth the effort of reading.
Any story, no matter the genre, should always have that big pay-off. It's the reward given to a reader or audience member. Believe me, a bad ending can leave a bad taste in one's mouth and word spreads quicker than a wildfire around these parts of the internets. Have a kick ass ending, 'nuff said!
Blake Snyder has made a five step finale beat sheet that you and I should and need to follow. It's done in a way far better than I could ever come up with. Click here for the full details and fix that damn ending!