The nice thing about the Switch is that it has something for everyone. So many genres of games available, and a lot of the games on the system are among the best of those genres.
Super Mario Odyssey and Super Mario 3D World are hard to beat in terms of 3D platformers. The former is a much more open-ended, Mario 64 style game, while the latter is much more level oriented and linear. They're pretty different from one another but both great in their own ways.
If you want a 2D platformer with a bit more difficulty, Donkey Kong Country Tropical Freeze is one of the best. Great gameplay and level variety is unreal.
If you're looking for a much more challenging 2D platformer instead, Celeste is incredible. Super tight controls and great use of its mechanics. Fast gameplay. Phenomenal soundtrack. Basically everything you could want in a twitch platformer.
If you're a JRPG fan, the Xenoblade Chronicles Trilogy is great. They each have loose references to each other but are primarily standalone games connected by their themes and gameplay structure. I'm particularly a fan of 3.
Also in JRPGs, Persona 5 Royal is on many platforms, but the Switch version is great and it's a hard game to top. Incredibly long, but in my opinion totally worth the full journey.
If you want something more strategic, Pikmin 3 Deluxe is a lot of fun, and it's gorgeous to look at. It's a real time strategy game that's presented in a very unique-to-Nintendo way. Also, it has a surprisingly great competitive multiplayer mode, so don't sleep on that if you have the chance.
Fire Emblem Three Houses is also a strategy game, but turn based instead of real time. Very lengthy, a lot of fun to delve into and get invested in the world and characters. It also has a lot of replay value, as there are multiple branching paths in the story that basically make half the game unique on each route.
For calmer/simulation style games, go for Stardew Valley or Animal Crossing. Can't go wrong with either one, though I'd say there's more to do in Stardew if you're concerned about that.
Super Smash Bros. Ultimate is one of the best party fighting games ever. So many characters to play as and a ton of content.
As you've said, Tears of the Kingdom is incredible. So is Breath of the Wild. I'd play BotW first if given the choice, just because Tears has much more complex mechanics, and it makes it easier to play if you're already familiar with the base mechanics from BotW.
There are more, but I'd say those are the big highlights for me. The Switch has an incredible backlog for someone just getting into it.