The one thing that this seems to miss, and for me what defines the "character" of a neighborhood as "walkable" or not, is how much of the space between buildings is for people vs. for cars.

So many of the photos here have skinny sidewalks for people and fat roads for cars, and a space like that is never going to be full of people -- the sidewalk is a place "to get from here to there", not a place to be.

Probably the best rule of thumb I've found is "Would I jaywalk here"? If an area is people-first, you have a lot of pedestrian traffic, little car traffic (because folks drive alternate routes), and what traffic there is travels at low speed. For car-first areas, it's a losing game of Frogger.