These are the first ones that came to mind:

- Playing Super Smash Bros. Brawl with VGC users.
- "A man chooses, a slave obeys" --> Such a great moment in gaming
- Staring at the wonderful scenery in Uncharted 2 (and yes that includes Nathan's buns)
- Playing Wario Ware drunk with my brothers and cousin --> Mindless fun
- The platforming bliss provided by Mario Galaxy 1 & 2

5 unforgettable memories from last gen:

- Playing wii sports for the first time
- Beating Zelda Skyward Sword
- Playing "Metallica - One" on Guitar Hero for the first time
- Playing Super Smash Bros Brawl with friends for hours and hours on end
- Having wii sports tournaments with uncles and aunts who never played a videogame before and seeing them enjoying the game so much

- Playing Gears of War 3 online 'till 4 am, with buddies, every single day of the week!

- Metal Gear Solid 4's final boss battle.

- Purchasing a Wii and being fascinated with what, looking back to it, seemed the future.

- Playing as Jack Marston, and watching him become everything he wasn't supposed to be. (Red Dead Redemption spoiler)

- Dragon's Dogma true ending.

In no specific order.
5-Suicide mission mass effect 2
4-The walking dead season 1 ending
3-Halo 3 MP
2-Bioshock Infinite revelations
1-GTA 4 playing online with best friend

1: Playing the Legend of Zelda Twilight Princess for the Wii and instantly loving it.
2: Call of Duty 4 Modern Warfare getting me into online multiplayer
3: Fallout 3 showing me the scope of next generation gaming with post apocalyptic awesome
4: Mass Effect 2 having the best examples of choice in video games
5: The Last of Us being the closest game to perfect I have ever played.

-Getting my Xbox 360 for free when I bought my PC
-Playing SSB Brawl with friends
-Moral pressures of Fallout 3. Won't spoil it -- but I had to do unspeakable things to escape. Couldn't avoid it.
-Finally "getting" Minecraft
-Delving into the beauty of Skyrim

PC gamers don't have gens.

1) Installing shadowfall and sitting through additional patches for online play even though ive not loaded multiplayer, not even once.
2) Watching both my PS4 and Xbox One struggling to attain 1080p/60fps
3) Thinking 500GB is "cute"
4) Unplugging my xbox one and using it to hold my bedroom door open (its still there)
5) Having to firmware update my ps4 every time i plug it in because i barely play it.

Oh last gen, you were so cute, now back to my pc.

My favorite memories of last gen:
-Playing the Wii (and Wii Sports) for the first time. It got me back into console gaming
-Playing Zelda Twilight Princess. First Zelda I'd played for almost 10 years.
-Playing Guitar Hero and Rock Band before going out partying, and playing after partying
-Playing various mini games on Wii with friends and family. Local co-op STILL rules!
-Discovering 3rd party games again, and playing a bunch of them: MegaMan 9, Batman: AA, Tomb Raider and more

It's been a VERY good generation for me =)