Candid Street Photography / Discussions

I spend a bit of time looking at the photographs on http://www.masters-of-photography.com. Call me a romantic but my favourite is this classic

http://www.masters-of-photography.com/D/doisneau/doisneau_kiss_full.html

The famous Kiss by the Hotel de Ville by Robert Doisneau 1950.

What is it about this photograph that makes it a classic?

I find this sort of question really hard to answer. It captures a candid care free passionate moment amongst a grey Paris back drop with everyone else just going about their everyday business.

To me it is the classic street photograph, and I marvel at Doisneau's ability to capture this moment.

Perhaps someone has a better view as to what makes this photograph.

Alternatively if you have your own favourite why note post it and tell us why you think it is special