To me a good image is one that strikes you, one you remember. I don't think there's a magical formula as to what makes pictures work. I've always appreciated the high finished image quality of a Salgado, or a Eugene Smith, but I like images by Moriyama, and others. Sometimes an image is great because its subject driven. Sometimes the subject is the photographic media itself, light, etc. But all I know is that what I tend to consider as the best photographs are ones that have something about that stands out. Another expansion of this topic is how does all that work for series of images or projects where its not one image. Like a book for instance. I think each has to come to their own conclusions and methods, and hopefully keep an open mind as to how other might approach it. I guess I'm saying something like I may not be sure I know what makes something work, but I know a good image when I see it, or at least what seems good to me.