It's Pikmin for me. Such an amazing series.

Advance Wars is another great one.

Warioware and Advance Wars get my vote.

The first Kid Icarus.

Punch Out is probably number one for me with its memory and reflex based gameplay that is deceptively deep. I'm not a big fan of the arcade titles but I've loved all of the home entries, with MTPO!! in particular being one of those games on the NES like Mario, Zelda and Metroid that just shouldn't have been that good way back then.

Very disappointed that the Switch still doesn't have a new Punch Out in its massive library of titles.

Definitely Kid Icarus.

But just because of Uprising, the story was amazing, the gameplay great and the Sakurai's charm and humour shone all the way through.

Advance Wars gets my vote but honorable mentions for F-Zero, 1080 Snowboarding, and Wave Race

Punch Out and Advance Wars are both amazing series.  I would love Nintendo to make more entries in either series.

I suppose Xenoblade is still borderline for the criteria of this thread. But I feel Xenoblade and Fire Emblem are too mainstream now in sales and acclaim recently to make most people's list. Shoot, I would've said Metroid was too small in spite of its acclaim but Metroid Dread and Metroid Prime Remastered have done very well. 

Some great picks so far!

As someone who grew up with Starfox on SNES and N64, and ranks both in my top 20 games to this day due to their epic space opera vibes, intense action, stellar soundtracks, and badass boss fights, I'll always have a special place in my heart for the series, even if there hasn't been a single good entry post-N64 in my opinion. 

Sin & Punishment would be up there too, as both games are brilliant and highly under-appreciated due to being rather niche. They're completely bonkers in the best way possible and gloriously intense, challenging, and varied.

Earthbound?