People playing on emulator years after the release won't understand what it was really like at the time, but those of us who played it as children know the truth: Super Mario Land 1 really is Mario's blurriest adventure ever.
As I understand it, each classic Super Mario platformer has these as their core themes:
SMB1: Alice in Wonderland
SMB2: Masks (from Fuji TV's Yume Koujou event)
SMB3: Japanese mythology
SMW: Dinosaurs
SML1: Ancient civilisations
SML2: Uhhhhhhh…… every wacky idea they had left??