Fire Emblem and Xenoblade, maybe Zelda too.

Got an NES back in 1988 and loved the console but not really Nintendo's first party stuff. I played a lot but they didn't really say my world on fire or anything. In fact, they were pretty simple and generic.

Then, Super Mario 3.

I didn't even play it when it first came out. But when I did,..Oh my God! Combined with the Captain N TV show and the Super Mario cartoons, I was down for life.

There are many Nintendo games that I love but only one can top them all.

Super Mario World. The game was fun through and through, every level with great design. The length of the game was great. The music was great, even at work I can sing the tune and coworkers will notice. Yoshi was interesting as well as the 2 player, trying to beat each other in levels. A masterpiece, that anyone should try.

I had a NES at launch so iv always been part of the eco system.

The Legend of Zelda: A Link to the Past.

I tell this story every year in the Top 50 thread. When I was young my aunt and my two slightly younger cousins lived a short street away from me. My aunt was an avid gamer in the NES and SNES days, and in turn my cousins would spend a lot of time playing video games while I only wanted to be at the playground nearby. I had played some games before though; Super Mario Bros. and Duck Hunt, the black box Soccer game, and perhaps other things like simple 2nd Gen games on my own mother’s old G7000, the Odyssey2 in America. However those were all casual plays, and in my mind it was a silly way to spend time. Young as I was, we’re talking 4 or 5 years old here, I also didn’t exactly know what I was doing.

When my aunt got the SNES she moved the NES upstairs for us kids to use, while the new SNES remained “off-limits”, though she wasn’t very strict about it. One day, I was probably 6 at that point, I came down the stairs in my aunt’s house, ready to go home after maybe having played Duck Hunt for a bit with my cousin, when she called me into the living room. She had something to show me before I went, and she thought I’d like it. I awaited curiously as she reset the SNES. I was immediately captivated by what I saw; the bombastic music of the opening screen coupled with a sword in front of a view of a castle was probably already enough to win me over; I had plenty of LEGO Knight sets and plastic swords at home. She started a new file, and my eyes grew wider with each passing second as the mysterious intro played. I couldn’t understand the English text yet, but I could understand the pixelated art of battling knights and monsters interluded with clips of a wizard making princesses disappear very well. Finally the game started, and my aunt made the character move out of the house you start in and I saw the most epic thing I ever saw in a video game; thunder and rain. This made such an impact on me, that I was all-in at that point; my mind had been blown three times already in the past five minutes. I wanted to play this game in its entirety right then and there, but unfortunately, my aunt only walked up to the castle and then shut off the game again. I’ve been a fan since that very moment, and Zelda is my favorite franchise since that very moment. Sadly though I needed to go home, for dinner.

I guess that would be Pokémon Gold. It was the first "complex" game I ever played. Up until then, I had only played 2D platforming experiences like Mario were you went from left to right pressing A to jump and B to ocasionally throw some fireballs. But this was an RPG. It had tons of text for a 7 year old like me, many "complex" mechanics both in battles and outside of them, puzzles, an interconnected world filled with things to do. It was so different than anything I played before. It was even overwhelming at times. I mean, I constantly got stuck even with very basic stuff (It took me days to even get the Pokédex xD). But with time, I learned to play and I end up loving the game. I put almost 500 hours on it. I became a Pokémon fan. And from that point on, you could make a timeline of my entire life using the next Pokémon main games as a reference in time xD

Thanks to Pokémon, I became confident trying new games. When my parents got me my GBA SP, I discovered Metroid Fusion and Zero Mission, Golden Sun and its sequel The Lost Age, The Legend of Zelda: Minish Cap... and in turn, I became a fan of all those series. I became a Nintendo fan.

So... yeah, Pokémon Gold started everything. Not only made me a Nintendo fan, but it marked the path for how my gaming journey would be. If it weren't for Pokémon, I may have not be interested in videogames today as much as I do. Now I'm not only a Nintendo fan, but an enthusiast of videogames in general.

Mario on the NES from playing it at my newphew's house. I was used to MSX at the time with mostly slow moving games, low fps and muted colors. Mario ran smooth with lots of color and much better controllers.

Smash Brothers Melee. Playing that at friends' houses as a kid made me want a Gamecube myself so I could play that game, and it made me curious about the various franchises that were represented,

Well, if we can go through our personal history on when, why and how Nintendo reached our heart, I think we need to have several approaches regarding our, at the time, knowledge of video games, how often we would play it (or still play it today), and other related stuff I guess.

For my perspective, and my personal story, my real first video game was actually Super Mario Bros, on an hacked chinese console my parents bought in Turkey and which was commonly called "atari" (oddly enough). We had 1 cartridge full of games, but the most pleasant game was indeed Super Mario Bros, so we would spend hours to play it. (Contra was aslo fine tho, we would play it with my brother).

And then, I saw several times my cousins playing Super Mario All Stars on their SNES (which I didn't own) and then Super Mario 64 (didn't own either), but I had a Game Boy (with my sole cartridge being Pokémon Blue). Got a refurbished PlayStation once the PS2 was released, played essentially the Demo 1 disc which was in it (at that time, games were really expensive and my parents wouldn't want to spend money on video games). But I had a PC, and that's when I discovered the emulation world, and would play several Nintendo 64 games on my pc (not an easy task).

And until 2014, I never had the opportunity to actually own a console (mostly played on a low-end PC), and that's when I bought a PS3 (to play GTA V) and then a Wii Mini with Super Mario Galaxy 2 (one of the best games I've ever played).

So basically, that's when I started to specifically choose Nintendo consoles and games over everything else, cause it reminds me my childhood and I still think playing on a low-end Nintendo Console is always way more pleasant than playing on a huge beefed-up gaming console.

And my dearest apologies for any mistake I possibly made while I was writing my post.

Had almost the same experience with that fake console that we, people living in the underdeveloped side of the world, called "Atari" with its 150-games cartridge. Every family possessed one for it being cheap, and it was the mainstream console that introduced gaming to everyone in my country, including adults. (Then came MASSIVELY the PS1 that sold extremely well because it was easilly hackable). 
So Duck Hunt and Mario Bros for me on that "Atari" (like evereyone in my country as i suppose).
Basically we didn't know that they were nintendo games due to the fact they run on a corrupted system. Nintendo was accidentally introduced to every tunisian home.

Then, Pokémon was aired on a french TVchannel (year 2000/2001) making me an instant hardcore fan of the series, and seeing all the ads compelled me to sweat really hard to get extremely high marks at school so i can get my gameboy and Pokémon Red (500 hours of play, i deserved that anyway).     
That same period, my uncle owned a SNES and my aunt a MegaDrive. Had a lot of fun watching them play games on both systems, but ended up playing SNES games more, and especially F-zero. Untill one day, my uncle rented the unique game he found in stores, and it had to be Super Metroid. He didn't like it, but i ended up playing it the whole summer spending probably 50 hours to beat it, and it was one of the best things i've ever played being one of the most challenging games at that time.

So yeah: Duck Hunt+ Mario Bros//Pokémon Red//F-zeo and Metroid for me.