COD4

Offline: Perfect Dark
Online: (hate to say it, because now I know that I was so stupid stupid stupid to be addicted to a never-ending game) world of warcraft

Goldeneye 64, by far. Hands down. I've spent so many hours in that game inviting friends over and shooting them for hours on end. It came to the point that during the last few days at my junior high, someone said they were bringing a N64 and I just had to take the chance to bring over my copy of the game so I can gun down my classmates as well. That was some of the best multiplayer experiences I've ever had.

Recently though? Halo 3. Me and my buddies tearing it up in Standoff? Doesn't get better than that. That's for sure.

This gen would be Halo 3.

Quake TeamFortress, StarCraft, SSBB, TeeWorld

Call of Duty 4:Modern Warfare

No contest:

Four Swords Adventure.

Only way to improve it is to make it more online-friendly, but even then it's a local title.

local: Winning Eleven 6&7, for 2 years I played these games every day at home and every weekend me and about 4 other friends get together in someone's house and play for hours.

runner ups : Crash Team Racing, Crash Bash, Super Mario Kart

Online: World of Warcraft, one of the best online games ever so much fun and funny moments.

runner ups: Battlefield 2, The Lord of The Rings: The Battle for Middle Earth II

Mario Kart 64 far and away.

joint operations ( 150 player battles on huuuuuge maps )
warcraft III ( still great today )
age of empires ( timeless )
mario kart 64 ( all successors never reached it )