Why has it become the norm to refer to photos that you like as 'stunning'? Not that I care. Over on Talk Photography someone raised the age old question of what makes a great photo, well 'the perfect' photo actually, but I guess they could have said 'stunning' too. Perhaps 'memorable' is a better word to describe successful photographs?
For what it's worth I reckon photos rely on four keys to be stunning/memorable/successful:
Content, timing, framing, technique. Possibly in that order of importance.
Content - which can be abstract or figurative.
Timing - this can mean waiting for the light to change when the subject is landscape, freezing a moment when the subject is less static, or just being in the right place at the right time by chance.
Framing - the composition of elements within the picture area create harmony or discord, balance or tension.
Technique - affects how the image is rendered, and works best when it is not apparent.