-The main reason I prefer SMB3 over the other Marios I have played, even Super Mario World--the eternal rival in the question of best Mario game--is the variety.-

I'm similar, plus SMB3 has a bit more challenge (SMW's challenge comes either late-game or finding the secrets).

-Kuribo's Shoe is probably the most well-known of those next to the angry sun, and I think it alone could justify SMB3's design approach. -

It needed to be in more levels!

Ditto more giant levels.