What have been the most surprising experiences for you in Nintendo?

For myself:

• - Playing Smash Bros. Brawl and realizing the physics were extremely dissatisfying compared to Melee
• - Mega Man 9 being realeased on the Wii Shop and actually being more fun for me than its predecessors
• - Wii Fit becoming one of the top selling games of its generation beating out traditional franchise staples

It was surprising just amazing Breath of the Wild turned out. I can't remember the last game I was so enthralled with.

Wii Fit being so insanely popular was definitely surprising. I think my brother had it and maybe a couple friends, and it seemed very meh to me. But I mean it was basically for the population that doesn't actually work out and thinks they can get in shape in front of their tv, which is most americans at least.

Wii / Wii Sports was a very surprising experience for me. I mean the fact that such a simple game could be so damn good and provide months of constant fun simply by having motion controls was pretty revolutionary.

In recent times, I would be said Splatoon and Zelda BotW.

Let's see...

- Seeing Super Mario World for the 1st time. All those colors and demo gameplay... :D
- Playing Mario 64 for the 1st time. 1st time playing a 3D game too, so my kid mind was blown.
- Seeing and playing Smash Bros Melee for the 1st time. Those graphics and fast gameplay..!!
- Seeing the Wii for the 1st time. It was a bright shining morning, with a bright Zelda on screen. And Wii sports was pretty awesome.
- Playing Trauma Center. Who knew a game about surgery could be so much fun?!
- Playing Splatoon for the 1st time. It felt so fresh and innovative for the shooter genre.

I think that covers it...?

Hmmm...
The Wii Virtual Console was a pretty major surprise for me; getting to play games I loved as a kid, as well as games I missed, got me back into video games at a time in my life when I had different interests...
The first two New Super Mario Bros. games showed me that sidescrollers could still be magical in a time of 3D and first-person...
Animal Crossing surprised me by basically being an addiction...
Kid Icarus Uprising rebirthed one of Nintendo's best forgotten gems...
Xenoblade went from not being on my radar to being one of my favorite games of all time...
And Splatoon and Arms demonstrate that Nintendo's future is in good hands...

I'll admit Lusamine's madness caught me off guard to just how extensive it was.

Yeah, this one is pretty high up my list as well.  The ability to explore every corner of every mountain and desert really is awesome.  Now that I've experienced it, it really bothers me when my character can't even climb up a small hill in many other games.  

Recently it has to be Breath of the Wild. I was fully expecting to be in the "not as good as the reviews say it is" camp but then I played it and got sucked in by this amazing game like I haven't been by a single player game in a long long time.

Eternal Darkness Sanity's Requiem, I was 8 at the time when I played that game, and it was the surprise for me of how in depth a game's story could entice me, it really spawned my passion for video games as a whole. Though it's technically Silicon Knights as a developer it's still Nintendo published. Plus, it was their first M rated title, so I'm gonna allow it.