Checklist for writers:
Are the hero and heroine different enough at the beginning to make their coming together a challenge?
Is the villain evil enough to emphasize the strength of the protagonist? Or take advantage of his/her weaknesses?
Is there a love triangle or a rival to make it a challenge for the hero to win the heroine or vice versa?
Are the supporting characters interesting/challenging to add to the interaction of the protagonist?
Is the problem difficult, personal and important enough for the protagonist to take on at the beginning of the story and see it through to the solution at the end?
Are there external and internal problems for the protagonist?
Are there enough challenges throughout the story to reveal the strengths and weaknesses of the protagonist and teach a lesson that needs to be learned by him/her?
Do you build to the climax and the final problem before the resolution and does the solution come as a result of a change in the character? What does he/she learn?
Does the plot proceed with ups and downs to challenge the protagonist?
Pacing should be varied. Fast pace with short sentences to give the reader necessary information and slower pace with more detail for the important scenes like an encounter, romantic interlude or confrontation with an enemy. Think vegetables and dessert. The vegetables are necessary but can be eaten quickly. The dessert is for pleasure and should be savored.
Is there a subplot and is it resolved? Are all the loose ends of the story resolved before the final climax or does the story need an epilogue?
Are all the clues and foreshadowing used by the end of the story? All questions answered, especially in a mystery genre?