The difference is that Super Mario World was made for one player. NSMBU was made for multiplayer and I really got the feeling that this is not for me who wants a single player game.
Now THIS is a good assessment. NSMBU is definitely designed with multiplayer in mind, but you don't HAVE to play it that way. I've never played it multiplayer and I'm fine with that. I do agree that it may make the game less appealing to some people, but I still think people should be a bit more open-minded about it all. The game's a tonne of fun.
I got it all, baby!
PS4, Switch, WiiU, XBO, PC
Vita, 3DS, Android
Top 3 this generation:
Bloodborne, The Legend of Zelda: Breath of the Wild, Dark Souls III