First Impressions!
Electroliner wrote, in part:
"I think the overall wow factor is the whole scope of the layout..."
I agree, and together with the overall theme, the impression a person gets when first arriving and looking at the layout - that 'first impression' - most definitely can be a wow factor.
In my short experience in visiting layouts, I am thinking of two layouts in particular that have tremendous wow factors when first seen as a whole, and their themes jump out at you.
PatrickH's layout - A beautifully done, highly detailed layout with beautiful terrain, hills, weathered buildings, fully sceniced dioramas, and in addition, it is a lot of fun to operate; i.e., run trains. What a sight to see when you first arrive!
Alan's (OGR As Man) layout - When you arrive and take your first look at Alan's layout, you can't help but to think 'Chicago', and if I remember correctly, that is what exactly what he intended. In addition to his fantastic skyscrapers (*) and impressive train station, he also has a tremendous amount of fine details throughout.
Another wow factor is what you don't see or don't know about some of the layouts. The obstacles, trials and tribulations that some of our friends in the forum have had to endure and overcome just to build a layout, are double-wow factors. I won't mention any names as I do not have 'clearance', to tell.
Just my 2¢.
Alex
PS. (*) The stories behind how Alan built each of his skyscrapers are wow factors by themselves as well.