I've played it. It's a good game, don't get me wrong, but after you play SMB2USA, the Japanese version just feels like a slight rehash of SMB1. It's rewarding if you manage to beat it, because of its increased level of challenge, but on the other hand "Mario Madness" adds some welcome variety. New graphics, new music, new gameplay, new enemies...

Hell, I'm kind of disappointed they didn't bring back this little guy for other Mario games

its wiki entry says he only came back for a GBA game and for Super Princess Peach on DS.

But Shyguy, oh! He deserves to be in more* than 3 or 4, he's special!