Super Mario Odyssey is a must-have game for the Switch. After the tutorial, you're thrown into the Cascade Kingdom and then you're on your own. It's your job to explore every part of the kingdom. The kingdoms in Odyssey are brilliantly designed so that they're not too small but are dense enough to encourage you to explore every corner of it. Linear levels like in Super Mario 3D World or Land have been replaced by these expansive kingdoms. The kingdoms also act as hub worlds for other smaller platforming levels, puzzle levels, or minigames. The design of the kingdoms is truly what makes Odyssey great.
Each kingdom has its own environment, brilliant music, unique NPCs, enemies, boss battles, regional coins, moons, and secrets. There are dozens of ways to get moons and though not all moons are equally challenging to get, the game encourages you to find moons in many different ways. It's a collectathon in the best way that it could possibly be. Even the coins are fun to collect. Then the moment that you've explored a large amount of a kingdom, visited several areas, and found several moons, you can advance to the next kingdom and have a totally new kingdom to explore.
If you're a Mario fan, you won't be disappointed by this game. Super Mario Odyssey changed the idea of a mario game similar to how Breath of the Wild changed the idea of a zelda game. It didn't replace the old linear mario games but rather expanded on them for a fresh, new experience. There are still toads but not every enemy is a toad. There are still 2D sections but the entire game isn't 2D. I've played through plenty of Mario games from New Super Mario Bros to Mario Party to Mario Galaxy and I can confidently say that Odyssey is my favorite Mario game of all time.
Super Mario Odyssey is just plain fun. You can play at whatever pace you want. If you want to collect coins to dress up as Waluigi, you can do that. If you want to collect every single moon in every kingdom, you can do that. Since the game isn't too challenging, I've been speedrunning it and it's incredibly fun because there are dozens of routes and the movement is insane. Odyssey gives the player tons of freedom of how they choose to approach the game. I can't praise this game any more than I already have but I can assure you that Odyssey delivers an experience that you can't get from any other game.