Back in the beginning of 2011 I also considered a great story?. And in 2006 I considered Short story first lines. A great first line does hook the reader. You can't show off your great story if no one ever reads it.
Here and now in 2016 I think the one thing that makes any story great is emotional complexity. This works for short stories, and for 'TV' shows and movies as well. For example, in a recent movie a protagonist has to chose between love and personal safety. The creators of this work successfully created a character, a person, that has a whole host of emotions. Personal safety would be the safer, and probably easier, choice. What does the character do? He does what he has to do.
As you write your stories, consider: do they have emotional complexity? Does your character have to chose between options he/she/it has strong feelings about? If not, work on it. Good luck!
The deadline for our first 2016 issue is Jan 15, midnight (US Moutain time). Get those stories in!