Wave Race all the way from me baby...
Not a Nintendo game, but i loved Billy Hatcher on Cube, a game i wouldnt mind seeing a follow up to. Very Nintendo-esque

Haha! I bought Billy Hatcher :D  it's so unique!  When I was a kid there were these machines you put a quarter into and an egg would roll down falling through crazy traps.  When it reached the bottom you got the prize from the egg.  So awesome yuji naka (sonic team) made a gamecube exclusive out of that idea.  A really great kid friendly game!

Fire Emblem and Pikmin. However both are becoming more popular especially FE

Wow. Both of these games look quite nice and stylistic!

Thing is, Killer 7 was conceived as a GC project, but due to low sales of it, it was quick-ported to PS2, kinda like RE4.

You began this thread with Sin and Punishment.

You have earned the Nintendo Seal of Quality.

Also, the Punch-Out!! series is great, although I doubt it qualifies as "underrated."

Wave race all the way, and could Rouge squadron be considered a Nintendo franchise?

It's extremely funny how almost all of the must-play Nintendo games being mentioned are violent Playstation-style games.

I'm actually mad at myself for neglecting to mention F-Zero...
And mortified that I forgot the Art Style games...
How many times will I have to mention Art Style before somebody tells me how right I am that these games are great???

I would agree.  The Punch-Out!! series is underated.  The original was considered a system seller for NES, and it's only 30 cents right now on Wii U.   But Super Punch-Out!! came at the end of SNES's lifecycle and was buried under other mega releases that year like Donkey Kong Country and Super Metroid.  It is free this month for Club Nintendo members.  And Punch-Out!! Wii is so terribly underrated it managed to sneak under MY radar.  I found out about it by searching in a bargain bin!