Four-star chef Eric Ripert checked out the burgers at McDonald's and Burger King to use as a pattern for a burger at his new D.C. restaurant. Part of what he learned is proportion is everything.
Just looking at the basic burgers at each of these chains -- particularly the Big Mac -- showed me a couple of very key things: First of all, the burgers are a perfect size. You can grab them in both hands, and they're never too tall or too wide to hold on to. And the toppings are the perfect size, too -- all to scale, including the thickness of the tomatoes, the amount of lettuce, etc. In terms of the actual flavors, they taste okay, but you can count on them to be consistent; you always know what you're going to get.
Ripert's findings dovetail quite nicely with my theory of sandwichcraft.