I believe that it is mostly about how you react to the subject matter before you. If you truly react and connect with the subject, have a deep respect for what you photograph it will come through in the print . I think that is why some photographers are so good at certain subject matter and may change and somehow lose that soul in the images. Others are exceedingly gifted in any subject they pursue be it landscape, still life, documentary or portraiture.
I have always enjoyed Ansel Adams landscapes, and I think any fan of his can attest to the soul displayed in his prints. Recently I had a chance to see a copy of a remake of a 1944 US camera publication of Adams work about the Manzanar internment camps called "Born Free and Equal". I have looked at a lot of photography in my day, but I think the portraits of the Japanese Americans it contains are some of the most powerful portraits I have ever seen. The concern for the subject and deep respect for these people that emanates from the images is incredible. the work of Eugene Smith and Weston are the same way.
I don't think technical aspects really matter with the "great" images. It is really a matter of finding subjects that touch you deeply in some way. I believe that your love and respect for the subject is what comes forward in a great photograph. Even the ones about tragedy and suffering.
When you see an artwork, read a play or book that resonates with you, has that degree of soul you are talking about, the artist has reached the highest level of accomplishment and communication. Maybe a better word is communion with the viewer. The greatest of art continues to radiate the artist's soul for centuries.
Keep looking and keep an open mind. Just like the rest of us.