A quick list of the games I own for it:

- Super Smash Brothers Ultimate. Already on your list, so hardly needs explaining, but it's excellent. The system is worth it for this alone for me personally.
- Fire Emblem: Three Houses. Fire Emblem is a strategy RPG series if you're not familiar, and frankly this is the best entry in the series bar none. Like Smash Brothers the system would be worth it for this alone to me - and I'm honestly surprised to be saying that, but Three Houses far exceeded my usual expectations for the series. The character writing and story is genuinely great, and it altered and added to the series' usual gameplay in interesting and fun ways. I'm on my third run through, both because I enjoy it that much and because I want to see all of the possible routes through the story. Highly recommended.
- Astral Chain. Pretty solid action game, though it starts out very slow, with your options in combat being extremely limited in the first few chapters. You play as a sort of super-cop who is tethered to a monster called a Legion by the titular Astral Chain, and you control both as a sort of tag-team duo. Can be played single-player or co-op with the second player controlling the Legion. Story's nothing to write home about but has a good moment or two towards the end. Soundtrack is pretty great though. I'd recommend it if you like the genre.
- Fire Emblem Warriors. It's Dynasty Warriors, but with Fire Emblem characters... though sadly almost all of them taken from Awakening and Fates, which were the two most recent titles before this released, so some names you'd probably expect to see aren't playable, like Ike and Roy. It does have Lyn though, which made me very happy personally. Anyway, if you like fairly easily cutting your way through hoards of enemies to fight bosses with Fire Emblem characters, this is a fun one.
- Super Mario Odyssey. Already on your list, so I'll just say it's very good, probably my favorite Mario game at this point.
- Mario + Rabbids: Kingdom Battle. I'll second DataNinja's recommendation of this. For a game that is basically stealing the majority of its gameplay from X-Com, simplifying it, and dropping all of the trappings of that franchise in favor of Mario and the Rabbids, this is a much better game than it had any right to be. It's just fun and funny.
- Pokkén Tournament DX. And expanded version of the Wii U title, this is a Pokémon 3D fighting game. Haven't actually played this version of it much, but it's fun if you're into either Pokémon or fighting games (it's the latter in my case), probably doubly so if you're into both.

Also, Bayonetta 3 is in development for the Switch, which would be another system-seller for me personally, since Bayonetta 2 is the best action game ever made in my mind and the first one isn't far behind. Even with it not being out (or even having a release date yet sadly...) I can be pretty confident that'll be one to recommend.