Similarities:
Peach gets kidnapped by Bowser (again...)
New move to learn at the beginning of the game
Stars/Moons
Low health sound
Lost health sound
Differences:
Galaxy:
Rosalina
You go to different galaxies.
Luigi?
Sad and touching ending.
Odyssey:
Cappy
HUMANS???????
More realistic
Music video trailer
What do the reviews say?
Galaxy 9.7/10 IGN.com and Metacritic
Odyssey 10/10 Edge Magazine and 39/40 Famitsu.
Overall:
I think if you want to get the Switch console, then this game is a must. You should have it pre-ordered, or else it will be sold out within the 10 minutes it sells. But, if you have the Wii U or the Wii, then you can still try to get the game, and you'll be amazed!