I enjoy the atmosphere and the impact this photo has from the first glimpse. The main protagonist, the man reading is strong but yet his surroundings are sufficiently alive and as focused as they should,to support the main theme. The tones are well refined and do not mix with each other in order to create an ambient (cannot describe it else) and non focused picture. Tones, shapes and cropping are excellent. The timing is a also an element which supports the photo. The people in the background looking towards the photographer depict the curiousness and interest of the everyday people seeing someone taking pictures in the middle of the street.(haha greek slung). But what makes it a great photo for me is that it inspires me to continue shooting from time to time.
From the other hand this is just the opinion of a graphic designer and not a professional photographer.
Hope it helped.