Why It Should've Been Terrible:
Realistically, any film whose cast requires a scarecrow, a tin man, a lion, flying monkeys and Munchkins, and whose sets include a flying house and a road made out of yellow bricks, should have been binned before a frame of footage was shot.
How It Became Great Instead:
Who wants realism? Here's the classic case of Hollywood throwing everything at the screen until it works, even if that meant hospitalising original Tin Man, Buddy Ebsen, with lung-coating aluminium make-up.