What do most readers look for in a mystery? Good points I hope to cover.
Draw a reader into your story.
Make the reader sit on the edge of their seat waiting to find out "who did it", and the characters so compelling that the story holds their interest from the instant they begin reading it. There's nothing like an unexpected finale.
As with any good story, both character definition and plot are essential. Do the characters lack enough detail to keep a reader interested? Read the story aloud and try to envision them as a reader would.
The same applies to the plot.
The place and events leading up to the mystery are just as imperative. If both are poorly represented, a reader's interest is lost most of the time.