Just to jump in, let's just accept whatever genre definitions people use so this doesn't become a debate over terms.
Fighting- Smash Ultimate- Not technically the best, but the best balance between accessibility and depth. And fan service out the wazoo.
RPG- Skies of Arcadia- Just such a likeable cast and a positive.
Rhythm- Guitar Hero 2- Because I'll never be able to play the solo from Hangar 18 in real life.
Fitness- Ring Fit
Platformer- Super Mario Galaxy 2. The pinnacle of what can be done with a simple set of mechanics.
Visual Novel- Phoenix Wright- I like yelling objection.
Action/Hack n Slash- Bayonetta 2
Adventure- Skyward Sword