For me it was Tetris 99. I'm a "seasoned" gamer so I've been playing Tetris most of my life but I had mostly lost interest in it, and didn't see how a battle-royale style Tetris game could work. 100+ hours later, I'd say it worked pretty well, and definitely reignited my interest in the core game!
Switch: SW-3707-5131-3911
XBox: Kenjabish