Everyone enjoys a good mystery, so why not have your students write in this genre?
This is a very specific rubric for writing and scoring a mystery short story. The quality of student work is sure to increase if you are willing to teach and provide this sort of rubric before the assignment is due.
It has a four-point scale for six criteria (twenty-four possible points). One point is given to those who submit their work on time. Multiply all points by four, to get the number grade.
This also includes an accompanying peer revision rubric so students can assess and give each other constructive feedback on their drafts.