Firstly, I'll try to describe the emotional response. When I see an image I really like, a feeling of pleasure rises up from inside me until it touches my lips and forms a smile. But images can evoke the full range of emotions from tears, to anger, to laughter. An image's ability to evoke an emotion is one of the measures of its strength.
It's fascinating that everyone reacts differently to images. In essence the image brings 50% to the party and the viewer brings the other 50%. Appreciation is the sum of the viewer's experience and the image itself. That's why some people can look at a print and it leaves them absolutely cold while the same print can have a profound effect on another person.
There are a few images which strongly affect virtually everyone because they sum up a powerful emotion or statement about the human condition in a universal way.
On the other hand intellectual appreciation revolves around understanding and acknowledging the context of the image, the implications of its content and the analysis of its aesthetics.
Overall when I see a good image, there's a feeling of recognition, a clicking into place of both emotions and intellectual understanding, which produces a sense of fulfilment and ultimately leaves me with a feeling that my soul has been enriched. I can't begin to describe how profoundly an image can move me, the deep joy it can give me as I discover its beauty. I really do love great photography.
Strangely enough the images that have the most profound impact are ones that I see in printed form. Pictures on the screen never have quite the same impact. The feelings I experience viewing a printed image are much stronger than seeing the same image on a website. The tangible print is the ultimate product. It completes the life-cycle from light reflecting off a subject through the lens on to the film or sensor, until it is again reflected light, this time from the surface of the print.
It's wonderful to go and see prints in as many galleries as you can, to look at photographic books and even magazines. That's what photography is all about; the final printed image.