To me at least this one is easy. Easter Eggs can be fun, but honestly usually at best they get a smirk or a nod from me, they are rarely really clever or funny enough to be memorable. There's really only one that comes to mind that really mattered to me. Made me smile and stop playing for a moment to process it because it had weight.

It was finding Remedy's ending to Max Payne in Alan Wake, "hidden" as Alan's manuscript of his latest novel about a character who is an ersatz of Max, narrated by the voice of Max.

Instead of being just a joke or a refrence, here's an easter egg that actually improves the game. No, it improves TWO games. It gives Max Payne some closure. We never got a proper conclusion. I never even played Max Payne 3, mostly because of DRM, but even without it I don't know if I'd ever touch that trilogy finale from a different studio, with a whole different setting and look. But Remedy cared enough to give us this little snippet of an ending. "Honey, I'm home." It's perfect.

But it also works for Alan Wake on a meta level. The game is all about such metatextual stuff. Creators and creations, authors and fictional characters. To have Alan be a fictional author of the character who is, basically, his predecessor as a Remedy game protagonist feeds into that theme and adds another wonderful layer to the game.

gotta love the halo 4 Conan O'Brien and Andy Richter Easter Egg talking about random halo lore weirdness in Mission 6: Shutdown

Christmas NiGHTS into Dreams was a limited release of the NiGHTS game for the Sega Saturn all the way back in 1996.
It featured a Christmas-themed level with the main character dressed as Santa.
But, the easter egg is the fact that you can unlock Sonic the Hedgehog as a playable character. And that's my favorite easter egg.
I believe it was the first time Sonic was playable in a 3D world, as Sonic Jam came out in 1997.
Despite the bite-sized content of the disc, it also had a number of date-specific events. For instance, playing the game on April's Fools lets you control the game's antagonist and playing on Valentine's, you're showered in heart shaped confetti.

My favorite is the Bridge of Death from Fallout 2. You meet a random stranger who proceeds to ask you a series of questions and if you fail you will die instantly. I've been a huge fan of Monty Python since forever and this made me laugh out loud.

My favorite secret is the "tuck tuck tuck" cheat in Age of Empires III, spawning in as many monster trucks as possible has some kind of nostalgia for me.

My favourite is an Easter Egg that never actually existed but has haunted me for years nevertheless.

I was in my first year of university and Super Smash Bros. Melee was all the talk amongst my friends. I mentioned once that I had managed, with a hell of a lot of effort and luck, to get to 14 kills using Roy in the Cruel Melee mode. Some guy piped in that he and his brother had managed to get 15 kills and that had unlocked the Sonic character. I didn't think Nintendo would EVER let a SEGA character into their game so I was pretty skeptical but my friend was adamant. Why would he make this up, I thought, this wasn't school playground bragging, we were adults now! We didn't do that kind of nonsense anymore!

So I spent months after that playing that grueling mode, trying to break my previous record and achieve the coveted 15 kills but never got it and every time I went back to my friend to complain that it was impossible he would encourage me to keep trying, he and his brother did it! So could I!

I never did it but even so many years later, with Sonic an actual unlock in the later games and knowing for sure that the character was never actually in Melee, there's a small part of me that still believes that I would have unlocked Sonic if I had just got that 15th kill in Cruel Melee.

The Mad Max jacket in Fallout 1
Nuclear Ghandi in Civilization 1

The "There are no Easter Eggs up here. Go away." sign on top of a huge crane in the docks, GTA San Andreas. As a kid, it really made me laugh and feel predictable.

The Easter Egg from Black ops I zombies with Elena Siegman's 115 in Kino der toten! It's incredibly nostalgic to me. There's also the Dark Souls bonfire easter egg and the Minecraft easter egg from Borderlands 2! Nice that they were both in the relatively same location!

For me it has to be the New World Computing Dungeon in Might and Magic VI: The Mandate of Heaven.

I remember you had to click on the bank building's wall in New Sorpigal to get a fly spell scroll that would allow you to reach one of the rooftops of the Buccaneers' Lair. Clicking again you would be teleported to the Dragonsand desert, in front of the Shrine of the Gods inside of which you could reach the New World Computing Dungeon by touching another wall.

This was the first secret I remember finding about in one of the earliest games I played with my father, and it has stuck with me throughout all these years.

Justin Bailey in metroid on the nes. I have no idea who this justin kid is but every boy in my elementary school knew his name. We had learned of his legend from a 101 CLASSIFIED NINTENDO CHEATS guide in the scholastic book fair. He tried to help me beat metroid but I still failed. But he tried and he will forever live on.

The giant head mode in Goldeneye for N64, multiplayer ofc

The san andreas' easter egg of that bridge that says: "There are no Easter Eggs up here. Go away"
I just find funny how someone took the time to hide such a silly thing. Whenever I think about it I imagine a dev writing it with a goofy laughter on the background XD

Mine has to be the AC Easter egg in The Witcher 2, where Geralt finds a dead body next to a haystack and wearing the Altaïr robes and Geralt says : " Guess they will never learn " and the player gets the assassin ability

One of my favourite Easter eggs is from Disco Elysium where in one of the thoughts that the MC has you can come across a reference to DMXs song Where the hood at.