It is subjective of-course, though technically it may be good or not, who knows? - It is not too light or dark and has enough detail in focus to make us think about what is going on rather than what the things in the photograph are. The colours are good with the various blues and yellows offsetting or reflecting each other, with the bold red of the skirt picking the woman out in contrast. The composition (though presumably encountered by accident) seems to reflect characters and emotions or attitudes portrayed in many classical paintings - possibly forming a bridge from the renaissance to the 20th/21st century?.
The thing about the "golden ratio" is that here it encourages the eye to move backwards and forwards across the image, treating it as a story rather than fixating one at one particular feature or other. I don't consider it to be, as often promoted, a magic number that happens to somehow encode beauty in an absolute sense. The picture has also been cropped to help with this.
Obviously people seem to like it - does one have to specify why?
Everyday the newspapers are full of photographs capturing contemporary events. These are nearly all technically excellent, but it is easy to go through them picking out the "great" photographs from the dross.
Eg. Today there are a lot of pictures accurately capturing Obama's tears over school killings, but I wouldn't say that any of them are "great". A great image has to make you feel connected somehow or spark an unexpected insight.
