I, too, have the same story. I was fifteen when the game was released, and it was the centerpiece for any gathering of friends. I have so many memories of that game and so many stories of fun times. I will go through a few here for nostalgia.
Team Snipers: Team Snipers was the game type that my friends and I all played in matchmaking. We were all rather good shots, except for my buddy David. David was an amazing -blam!- sniper. I remember watching this -blam!- single-handedly go toe-to-toe with team of four level fifties. But, I had never the opportunity to play him. Until one day, when a bunch of friends were gathered when one's parents were out of town, and someone abandoned their controller after seeing the silver rifle's gaping maw entirely too many times. So, I hopped on. Now, I was not nearly the shot that David was, but I could dodge a damned bullet like there was no tomorrow. I had played Halo: CE for the PC on dial-up for years, so I had plenty of practice on how to move in order to avoid bullets. It was nice to hear him yell, "Would you stand the -blam!- still so I can shoot you in the face!?" from a level fifty sniper.
Rumble Armory: Rumble Armory was my favorite matchmaking game type of all of the Halo games, and sadly, it was only around for a month or so. Rumble Armory was an FFA match where one weapon is chosen at random and that is the only weapon in the entire match. And it could be any weapon, from Swords to Plasma Pistols. These matches were always incredibly chaotic and, from playing Halo: CE, I loved it. But my favorite variant was Rumble Needlers on Gemni or Midship, because I was incredibly deadly with both Needlers and Plasma Grenades. It inspired the game type my friends and I called Snakes N' Spiders.
There was a time that my friends and I played Matchmaking for twenty four hours straight, by accident, without leaving our little room. We had managed to clean a disc that didn't want to boot and didn't want to stop for fear of it not booting again... until I accidentally bumped the system and turned it off. We looked at the clock and it was the same time, the next day.
I miss the grenades from Halo 2. I remember playing Rumble Pit, and I did terribly, scoring seventh place in Rumble Slayer on Warlock. I was using my friend's account and he got he didn't want to watch me play badly and wanted me to hand him the controller. I told him no, and that I would play the next match with nothing but grenades to make it interesting. It was Rumble Rockets on Lockout. I fired not a single rocket and scored nineteen kills with eleven sticks, coming in second place. I can still find those matches in his history, though the actual game data is missing.
And fireworks were more fun than hell. I could bounce stickies around any corner of Lockout, though that's nothing compared to the things I saw people do on YouTube.
Anyway, that's too much nostalgia for one night.