I think what does create the sheer impression of size is the wing and the height. With merely referring to the memory side of my brain the A380 is 2m or so longer than the 747-400 and shorter than the A340-600 by about 10 or so metres.
I do hope this is a great succes, the world needs two big players on the manufacture of Airliners (although there are many other smaller firms out there).