I am fan of original Helldivers, with its twin-stick shooter approach and local coop 4 player mode - so while I recognize the appeal and quality of Helldivers 2, it's not the game for me and honestly I didn't expect it to succeed as much, so that came as quite a surprise.
On the other hand, Palworld, which I only watched my kid play, with its pretty average gameloop and execution, and its "inspired" art feels like fairly expensive and elaborate prank - so its success definitely comes as bigger surprise to me.