The city centre of Cologne underwent a disastrous redevelopment after the war, mostly thanks to the RAF who bombed large expanses flat, though thankfully missing the cathedral. Somewhere the planning went awry and the core of the city is sadly lacking in something.
Atmosphere is a very intangible thing.
More likely, it is a synthesis of all three. The problem with Cologne is that it doesn't seem quite sure of what the function of the Altstadt is. There are plenty of shops, but it isn't really a shopping mecca. There are enough bars and resataurants, but they don't work together to form an entertainment quarter. In truth there's a bit of everything, but so mixed up together so as to be seriously diluted.