Does it get better than the very first part of the game? Haha, yeah.
Not really. It's pretty much the same thing over and over, just with different enemies. 'Fight boss, get hasty bit of backstory, move on to next world, fight enemies, etc.' The little bit of backstory for each boss, sans Bowser is pretty much the same, too. *Insert Creature/Character* gets a hold of a royal sticker and flips their ****, commence mashing the A button to win each battle, repeat for pretty much every remaining boss. The story doesn't get better either as there's next to nothing to build upon and nothing is added, unless "Mario goes here" counts.