As I mentioned, I am a member of the Short Mystery Fiction Society, and as such, I get to vote on the nominees for the Derringer awards. There are four lengths - flash fiction, short short stories, long short stories, and novelettes. There are five stories in each category.
I have been a judge in the past - reading ALL entries in a particular category and scoring them to help determine the finalists. I've done script reading, and judged scripts for competitions too - but there is nothing quite so eye opening as having to read and rate ALL of the entries in a competition. Because if you only have to read some of them, you never really know if you got an average sampling, if it was below or above normal.
If you read three stories, one will probably stand out. If you read ten, you may want to give credit to three of them. If you read a hundred, and they are all published fiction so they're all well written, and you know that only five can make the cut, then you start to realize that you need higher standards. You need to find a way to realistically score that top ten percent
It is a great exercise to force you to examine what makes up an exemplary story. What's the value difference between a perfectly executed but relatively easy plot, and an imperfect plot that may be trickier to pull off?
My answer to that is to say don't worry about how easy or hard it was to write - how successful was it for the reader? Does the imperfect plot actually touch the reader in some way that makes up for the imperfection? If not, it doesn't matter how much of a virtuoso the writer seems to be. But you have to choose your own criterion - and no matter what, there will questions that you did not anticipate.
So, I challenge everyone out there to start scoring the things you read. Not just an overall grade, but on plot, characterization, setting, meaning, voice, ending, and add a fudge factor ("overall storytelling" is a good one). If you want to get good at writing short mystery fiction, then get yourself a bunch of issues of Ellery Queen or Alfred Hitchcock's Mystery Magazine. Read through all the stories and pick the top five and rank them. Comb through the smaller magazines and web sites and judge them.
Don't critique them, judge them. And don't just pick the ones you happen to like - figure out which are most deserving on a more objective scale.
(And by the way, by the time you are done, you will have a good idea of what kind of fiction that magazine likes.)