Not really fondest but first thing that  came to my mind

I'm pretty sure I've told many of these already, so I guess I'll just go over them briefly.

- Getting the gamecube for X-mas, along with Smash Bros Melee, playing it a ton X-mas morning, and discovering Falco was in the game.

- Seeing the Wii for the 1st time on a bright morning, and Zelda TP was running, and it looked awesome.

- Playing Wii Sports with everyone in our little dorm area.

- Having a gamecube on 24/7 on in the living room, with 4 controllers and a copy of Smash Bros running. People played it throughout the day, all day.

- Having game nights at my place, and play many diff MP games, including 8 player smash days.

When I got my Nintendo 64!!!!!

Also, good to see curl's doing this, since you've been overall pessimistic for a lil while now.

So, so many. To pick one would have to be opening my SNES Christmas Eve 1991. It was breathtaking.

My family wasn't well-to-do but when I asked for that hot new Nintendo all my classmates were talking about back in 1986 I actually got it during the holidays. It was the beginning of a beautiful relationship. I bought myself the Gameboy when it came out and I was estatic about being able to play on the go.  Not many other kids had one so I felt empowered being able to play Metroid II, Tetris and other games you couldn't get elsewhere.  Lightening struck again when I got the Super Nintendo in 1991.

I bought myself a Wii U in 2013 as a gift to myself and rekindled this old flame.  Nintendo really makes great products.

So many great Shared screen games over many years with Nintendo. Those were always the best. :)

My fondest memories were playing Smash Bros. Melee and Mario Kart Double Dash with my college buddies.

I actually met them when they were playing Mario Party 5 with the dorm room door open. I asked to join in and someone handed me a controller. Joined in mid game with the least coins and stars made a sweet comeback and won.

Mario Power Tennis was also a great time with the guys. SSX Tricky. Super Monkey Ball (Playing Monkey Target). X-men legends 2, was awesome too. So, many good times.

With Wii Sports I shared great times with a ton of my family members.

Fortune Street was pretty popular with me, my sister, and her friend.

Nintendo gave us a legitimate alternative to board game night that was so approachable and fun without being shallow.

Truly, an art of shared experiences.

I appreciate that.

:D

There are so many for me, so I'll boil it down to the two biggest.

The first, my introduction to video gaming via a Super Nintendo and Starfox in Christmas 1994. To my child's mind, it was like playing Star Wars in virtual reality.

The second, the first time I played the Wii, in 2009. Using my own physical movements to move my character and swing a kendo stick in game was mind-blowing, it felt downright futuristic, like something out of Star Trek, but in real life.

I've stopped looking at reviews, and I've been happier with my purchases since. 

Playing Street Fighter II: The New Challengers with my brothers and dad when I was really young.
Playing Super Mario 64 the first time.
Watching my brother play through Ocarina of Time.
Playing Wave Race 64 and Mario Kart 64 multiplayer.
Getting to play as Zelda in Super Smash Bros. Melee.
Playing Paper Mario and Paper Mario: The Thousand Year Door.
Getting a Gameboy Color and Pokemon Yellow on my 10th birthday.
Waiting in line for 12 hours with my brother to get the Wii and Twilight Princess at midnight on launch day.
Beating Twilight Princess, which was the first Zelda game I beat by myself.
Obsessing over every piece of news and rumors and footage and trailers of Skyward Sword for five years and then finally getting to play it.
Playing all the way through Xenoblade Chronicles, which was at the time BY FAR the biggest/longest game I'd ever played, and it instantly became my favorite game ever.
Finally beating Ocarina of Time so many years later on 3DS, with the remake capturing how it always looked in my head. (I was too scared to do the Forest Temple as a kid because of the wallmasters, lol!)
The January Nintendo Direct where Iwata talked about Zelda Wii U the first time and showed the first trailer for what would become Xenoblade Chronicles X, which started my next three year period of obsessing over every sliver of news about that game.
Playing over 150 hours of Xenoblade Chronicles X in one month, between college semesters (the PERFECT time for it to release), pretty much 5+ hours a day. And it was amazing.
Playing 400 hours of Splatoon, and lots of Black Ops 2, Mario Kart 8, and Super Smash Bros for Wii U with two of my best friends.
Going to see The Legend of Zelda: Symphony of the Goddesses twice with my buds.
There's so much more. Seriously. And specific moments in games too. I could write a really long book about it all haha.