Super Mario Odyssey is officially the best game on the Switch, and reason enough to go out and buy the console. Seriously.
I'm only a few worlds in, and I already feel like a kid again playing Super Mario 64. Odyssey brings back all of those amazing feelings of playing a platformer in this 3D open-world-esque environment.
There will be more of a review to come later, but since the game is 'that' good, I have to get these initial thoughts out just in case it helps push some of you on the fence over onto the side of fun.
I was originally worried that the cap mechanic would be stupid and weird, but it works. Mario throwing his cap (named Cappy) to break blocks, interact with the environment, act as a jump boost, or possess objects/enemies/creatures has added immense depth to the platforming elements present in this 3D platformer style.

Actually taking over and possessing things has become really fun. You start off taking over a frog to jump higher, and then a T-Rex to break things, and before you know it you're a cactus and a ball of electricity and a pair of binoculars. My favorite so far -- even more than the T-Rex -- was possessing a Bullet Bill and flying around.
The world design has been phenomenal thus far. In just a few worlds, Nintendo has redeemed themselves from some of their recent so-so Mario projects, and especially from Galaxy, which I really did not enjoy.
These worlds are bigger, more involved and full of puzzles, and provide plenty of secret finding angles to explore.

One feature of the worlds that just made me smile was the 8-bit stuff woven into the 3D world. You'll come across these flat murals that are actually interactive 8-bit scenes you have to enter and then seamlessly jump out of -- and enemies can jump out of them too!
That's all I got for now! Get Super Mario Odyssey. It's simply cap-tivating.