I'm judging a contest myself, and I took advice from P.J. Coldren's comments here yesterday as a starting point. Having read two entries, my mind centered this morning on plot.
If I had to choose the most important element for me, it would be plot. I appreciate beautifully written prose and lovingly rendered characters, but if there's no plot or a bad plot, who cares? I suppose for literary fiction we can allow the character study novel or the moment-in-time study, but a steady diet of those would drive me crazy.
I need for things to happen in a story, whether I'm writing it or reading it. One entry I've read shows that the author has a sense of the whole, and each of the story's events moves toward that. Good job.
However, the other entry has the "kitchen sink" plot, in which so many things happen to the protagonist that the reader is overwhelmed. Individual events, catastrophes, threats, and perils are thrown in one after another with little explanation and no real thread of logic. Readers are expected to piece it together and figure out why it happened. In such cases, I think the author is trying for excitment but creates instead either event-fatigue (Think "action" movies where so many cars, helicopters, and armored trucks blow up that you lose track ) or disbelief (Even Rambo would have to take a nap or a potty-break at some point.)
Events as events don't work; there has to be a plot overview. I guess we all tried reading those romances back in the '70s where the woman got raped every third page and just went on to the next challenge because she was "spunky." No realism there, no matter how "exciting" you consider rape to be. Obviously some like the over-the-top action story, but reality keeps knocking in my head if it isn't done really, really well.
Balance would seem to be the key. (Gee, that could be a metaphor for life!) Things need to happen to the person that are interesting, things that require him/her to make choices and face danger, whether emotional, societal, or physical. Readers' tastes vary on how many such events or how much danger is enough. A good author keeps the inner logic of the story, so that danger doesn't come along just because. Plot events have to arise from the situation, the characters, and the other plot events. Even if you're a pantser, not a plotter, you have to keep that linear movement in the back of your mind. Leave out the kitchen sink, those plot events that don't move the character closer to the end goal.