Ignoring the lack of updates if the game is buggy, games back then were also more focused on quality and make gamers replay the game with unlockable features based on skills, not money. I can't count the number of times I played Metal Gear Solid games over and over to unlock new features playing the hardest difficulty and with handicap features, and also to find Easter eggs. Speaking of Easter eggs, you'd lose a number of hours exploring every nook and cranny finding them!
Couch multiplayer and LAN parties had a sort of friendly atmosphere that is sorely lacking from most online multiplayer today. Folks are all business, no fun. Even in casual modes people get mad if you fool around.
I miss open server browsers. I had a few servers I would frequent for UT2k4. It was nice just bouncing in for a few rounds. People were there to win, but between teams being shuffled between games and no real ranking system, no one was really a tryhard.