The photos that mean the most to me are the ones that are alive with potential meaning. Each person's interpreatation may vary but there is a possible narrative or implied symbolism that will inspire further observation and consideration. In photojournalism you want the story told in pictures. In art photography the story or meaning may not be quite so clear.
But there has to be content, composition, light and line that welcomes the eye and imagination again and again. These are my criteria anyway.
Sometimes I know I have something. But often, as in the case of, "Dog On Beach", this recent photo, I'm left wondering, "Is it just me?".