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??
I feel like all the sequels - 2, 3, and World - succeed at feeling like "a big adventure", but 3 and World both do so on a macro level, with the map screen and short one-note levels, whereas 2 is more "episodic", where each level is an adventure in miniature.
I feel like Super Mario Bros. 2 is the one game whose legacy was actually harmed by having Mario in it… it can only ever be compared unfavourable to both 1 and 3, even though its levels have completely different pacing and design goals.
Everyone talks about SMB3, but to me Doki Doki Panic is where Nintendo starts to break out the memorable platformer level designs… riding on a bird through 6-2, climbing up through a hollow tree in 5-3… even the little shortcuts in 1-1 and 3-1…
*forty minutes after jumping on a shooting Birdo egg to cross the ocean to the fortress in 4-3 of Super Mario Bros. 2, only to discover that the egg missed the fortress by like five degrees* Yeah, nah, I still think this plan was foolproof and no one could have predicted this