Maybe a "spoiler" if you care about unlockable content being a surprise but one of the worlds that unlocks after you beat the game lets you revisit boss battles, and they're remixed and harder. These are the best boss fights in the game.
This game has been a very good time waster, which is something the last few Marios weren't. They were over fairly quickly, and I didn't have a ton of interest in going back for stars once I finished them. So far I'm 25 hours and 430 stars in and there's no wall. I'm still unlocking stuff at a steady pace. Once I hit 500 and beat all the stages, I'm probably done though.

