The variety of the gameplay in Super Mario Odyssey is certainly one of it's most defining features, and it's easy to say that you're never really doing the same thing at any point in your adventure.
From taking the role of a massive piece of meat, to jumping around in zero gravity, Super Mario Odyssey never has a dull moment. It seems like one of the primary missions of the game's developers was to be constantly surprising you with new things to do.
This level of variety can be seen in every aspect of the game. From the music, to the worlds you visit, Super Mario Odyssey is extremely varied. That's not always something you can say for the rest of the series.
Breath of the Wild does struggle somewhat in this regard. Combat and exploration are such huge aspects of the game but they don't really advance all that much and mostly follow the same pattern. Variety isn't Breath of the Wild's strongest point.