Single player - F-Zero GX. The skill cap in this game is astronomical - mastering it akin to mastering a musical instrument. There's nothing else quite like it.
Multiplayer - Smash Ultimate. The amount of unique character matchups and interactions is so massive that there's always something new to see.
Agreed. I plan to make some posts around June 29th in the subreddits I frequented offering their alternatives in the fediverse - right before the 3rd party deadline.