It depends what you're interested in really and if you own any other consoles! A lot of the bigger games haven't come out yet so there a lot more smaller downloadable ones at the moment, some of which are on the other consoles too.
Granted, I don't have a Switch yet but some other than Zelda and Mario Kart I'm personally interested in are:
Cave Story+ - 2D Action platformer. I loved the original Cave Story on PC and would be awesome to have it on the go and with the new graphics style.
I Am Setsuna - Traditional Japanese RPG. This has been released on other things but looks pretty and I'm a sucker for these kind of games.
Mario + Rabbids Kingdom Battle (August)- Turn Based Strategy. Looks absolutely ridiculous and fun!
Metroid Prime 4 (2018?) - First Person Adventure. Only an announcement for this yet but Metroid Prime is one of my favourite games ever.
Rime (later this year) - Adventure/Puzzle. In the style of Journey, The Last Guardian etc. Again, has been released for other consoles but looks really beautiful.
Shovel Knight - Retro style 2D platformer. It's been released on pretty much everything else but I haven't played it yet and people seem to love it.
Snipperclips - 2 player puzzle game. You cut out parts of the other player to solve puzzles, looks great!
Sonic Mania (August) - 2D Platformer. Say what you want about Sonic games but this looks amazing with really cool music. I hope it lives up to what's been shown so far. Also staying far, far away from the other 3D Sonic game.
Splatoon 2 (July) - Multiplayer shooter. I didn't have a Wii U either so didn't play the original Splatoon.
Super Mario Odyssey (October) - 3D Platformer. Some people don't seem sold on the hat mechanics but I liked Super Mario Sunshine for gamecube so again I'm looking forward to this.
Yoshi (2018?) Platformer. Only a trailer so far, no date but seems like they've taken the wooly world of the previous game and added cardboard!
Yeah, so if I had a Switch that's what I'd get!