Not quite a pure platformer like Mario or Sonic.

Yes, both Hollow Knight and its sequel Silksong are exactly Metroidvania games. More on the genre of Metroidvania: https://en.wikipedia.org/wiki/Metroidvania

Silksong seems to be having great sales numbers + player count so far. They've topped the Nintendo Switch eShop as the #1 selling game. And also had a peak concurrent player count of 587,150 on Steam a few days ago. Pretty amazing numbers for an indie game.