90 New Pokemon (123 if you count Regional variants)
Z-moves return and are a Joycon gimmick
Regional variant Pokemon for Gen 2
Gyms are back
Elite Four are traitors later in the game and turn bad
Starters are-

Grass/Bug type praying mantis
Fire type Squid
Water type Porcupine

Legendaries are Ghost/Normal Wolf and Ghost/Fairy Moth like creature