Reaching the campus battle in Gears of War, then becoming addicted to the multiplayer. Then, when my friends and I were on wave 50 of Horde in Gears of War 2, calling out our targets so we could concentrate all of our fire on single enemies at one time in order to be our most efficient. All of us, huddled behind the same piece of cover stacked on each other, with a smattering of boomshields out in the open space before us, trying like hell to defeat the final wave. We did it and it was amazing. Gears of War 3 would repeat this moment, but do it even better with our fortification building.
When I was watching the ending/credits for the first time in Marvel vs Capcom 2, having just taken down Abyss with my mighty team of Strider, Ryu, and Akuma. It felt epic.
Carrying Ellie out of the hospital in The Last of Us.
The first time I heard the guitars kick in on the Clock Tower area of Castlevania: Symphony of the Night.
The first time I head pulling off an insane combo on Maya's stage with the vocals reaching their climax in the background music of Killer Instinct.
The first time I drove the warthog to safety during the finale of Halo: Combat Evolved.
My first day of playing Quake III: Arena on Dreamcast. I was blown away by the visuals, the music, the frantic action, and it was the first game I ever played online.
My first time completing Soul Calibur I knew it was something special. Soul Calibur II cemented the series' legendary status for me.
Watching the intro to Tekken 3 on Playstation got me super hyped and from there the game just continued to impress. It was non-stop amazing.
Hearing the song in the background of 3-7 Speedway in Daytona USA while racing past the colorful track under a beautiful blue sky.
Running around in Hyrule Field for the first time in Zelda: OOT and just sort of marveling at the feeling of freedom.
The first hour or so of Metal Gear Solid. It was so cinematic and advanced it felt years ahead of every other game.
The first encounter with the T-Rex in Tomb Raider on the original PlayStation.
Watching Damned whistle for henchmen to come help him in Final Fight.
Impaling somebody with Scorpion's spear in Mortal Kombat and hearing him yell "Come here!" for the first time. It was the coolest thing I'd ever seen in a game. (I was about 12)
Reaching the speederbikes in Battletoads for the first time.
Seeing 4 players each in control of one of the turtles, all on the screen at the same time, whooping Foot Clan ass in TMNT: The Arcade Game.
Playing the first stage of Super Mario 64 and being floored by the fact that you could run anywhere at any time. It was pretty mind-blowing.
Fighting the first Barons of Hell in Doom. My first experience with this game was owning it on the Jaguar. It rocked my world as it was only the 2nd game I'd ever played in the first-person perspective (Wolf being the first).
Lots and lots of great memories there. That's not even the entire list, I'm sure. I could sit and think about this for hours.... Great thread!