Disney's main innovation and departure in 1955 was to replace the traditional "back wall" with, in fact, no wall and a beautifully designed manufactured landscape. Trompe l'oeil becomes terrain, the "scenic switchback". The earliest example of this may be the Jungle Cruise, but I think the most beautiful one is the Matterhorn Bobsleds, which is an exciting, fascinating wait in line by virtue of... yodeling music and manufactered rocks.The Third Queue
But for all that, honestly, we don't think of Disney's best queues as being plain switchbacks, even if they secretly are. If we cut the roof off the Florida Pirates of the Caribbean queue and look in, we'll see that the switchbacks are unpredictable because they wrap behind walls and around scenes, they're actually pretty much just like what still graces the front of Snow White's Scary Adventures (see below). Even the beautifully linear Space Mountain and Indiana Jones Adventure queues eventually reach switchback areas, just not immediately or obviously. These queues, the "secret switchbacks", are a later innovation on the part of Disney and are what is generally thought of as the "themed queue", atmospheric treks which set up some component of place or atmosphere, indicators of an advanced state of themed design. In the context of Disney-designed attractions, this mode was more or less invented for the Florida Pirates of the Caribbean, although Disney did not always use it for every attraction. Big Thunder Mountain Railroad, for example, is more or less a simple "scenic switchback" queue, at least in the original design of the attraction (built in Florida in 1979).