My personal favourites on the Switch are Metroid Dread and Mario Odyssey, so I'd definitely recommend those. Another game I love that I don't see mentioned very often is Cadence of Hyrule, it's a crossover between Crypt of the Necrodancer (a rhythm roguelike) and Zelda. With Zelda soundtrack of course! If you like 2D Mario you'll probably want to get Mario Maker 2, but be aware that it's not worth it if you don't want to pay for a Switch Online subscription since wouldn't be able to play other people's levels.

Mario Kart 8 and Smash Ultimate are both really good, but I'd only recommend them if you intend to play multiplayer. Especially local multiplayer is fun, but online works too of course (again, needs a subscription).

The Switch also has some cool remasters and remakes of games you might have missed, like Zelda: Link's Awakening, Metroid Prime, Zelda: Skyward Sword, or the first three Pikmin games (the fourth one comes out this week and I'd be surprised if you needed knowledge of any previous games to play it). Pokémon Brilliant Diamond/Shining Pearl were a bit lacklustre, but if you like classic Pokémon games they might still be worth it. Just don't expect a lot of new stuff if you've played the originals.

I've played them on PC, but Stardew Valley and Celeste are some of my favourite games. If you haven't played them on another platform already check them out as well!