Super Smash Bros. for Wii U is possibly the most underrated Smash of all-time.
The original game still gets some love because of nostalgia, OG status, and a very small tournament scene.
Melee is loved by not only casuals, but namely the small amount of tournament players.
Brawl gets some love for Subspace Emissary and bringing Snake and Sonic to Smash.
Smash 3DS gets some love for being the first portable release and Smash Run.
Ultimate is the most recent title and most packed with fighters and stages.
But Wii U? It gets lost in the shuffle. A lot of what makes Ultimate amazing is in Wii U, but Ultimate outdoes it in almost every way. I do like trophies and a few stages like Jungle Hijinxs. I have tons of fond memories of Wii U and still put more time in it than Smash Ultimate. Admittedly, I played more local multiplayer in 2014 and played less games overall.
Wii U had the best Smash for 4 years.

Bayonetta 2. Breath of the Wild is so over rated it's painful.

Man, WiiU had sone absolute bangers despite its poor reception.

Although I consider it more of a Switch game, Breath of the Wild is the winner here. It’s an amazingly immersive, inventive experience with an unmatched sense of discovery and a perfect balance of structured fun and player improvisation.

As for second place, I’d go with Mario Kart 8. It’s easy to forget the 2014 release since we now have the far superior Mario Kart 8 Deluxe, but the vanilla version is still better than 99% of racing games.

Gonna give a shout out to Yoshi's Woolly World, just because I feel it won't get much of a look in.

In reality, I'd opt for Twilight Princess, Wind Waker, and Breath of the Wild over it (although I only ever played BotW on the Switch).

I only played BotW on Switch so I am going to conveniently not count or vote for it. I'm a sucker for the series so I have to go with Splatoon. The Nintendo twist on the 3rd person shooter that feels like so much more. Between the 3 titles I bet I have logged 4000 hours covering the floor in my ink. It is the most fun I've had with a shooter since GoldenEye.

Xenoblade Chronicles X for me. I don't think I've ever been so invested in a world like this before or after. It went on to be in my top 3 games of all time. Not to mention the wait for this game. We got a reveal and then little piece of info over the course of a few years. It was torture, but it more than paid off.

I voted for Breath of the Wild, but it came so late in the console's life that I feel that Mario Kart 8 is probably my favorite regarding the legacy of the console.

Tropical Freeze, baby!

I generally get Nintendo console for two things - Mario Kart and Zelda (everything else is bonus).
MK8 didn't disappoint.
BotW, to a degree, very much did.

if any games released on it counts, ZELDA BOTW without a questions. but mario3D world is up there.