I haven't beat the fourth yet, (I am currently on Gooper Blooper) but I will have to say it is my least favorite so far. There are pretty much no intersting characters who aren't Toads. Also, no partners either. I really wanted a Chain Chomp partner or maybe a Snifit partner. Kersti is okay, I mean she does have her
SHINING 
dk

moments, but she's just not interesting enough to warrant a total lack of supporting characters. However, Snifit or Whiffit was pretty cool. And guys. Shyguy Mariachi band. Just...woah. Nintendo. WHY DIDN'T YOU MAKE THESE GUYS THE MAIN CHARACTERS. IT'S A BAND SHYGUYS IN GOD DAMNED SOMBREROS. THE POSSIBILITIES COULD HAVE BEEN ENDLESS. But still, a very good game. I just wish the boss battles consisted of more than going up against a super-sized enemy and hammering him with all the thing stickers you can fit in your inventory.