What was the first online game you ever played?

Hard to recall for sure, but possibly a MUD (can't recall the name of the MUD), on a BBS called "The Abyss".

Before that, modem-to-modem with a friend, ...probably Warcraft: Orcs and Humans.

P.S. @OP, if you were on PlanetDungeonSiege before and for a little while after Dungeon Siege's release, you may've seen some of my posts or a video clip of beta gameplay! (different pseudonym back then though). :D

Team Fortress Classic was probably my first real MP addiction though.

probably Trade Wars 2002

chu chu rocket

Diablo or Interstate 76, whichever came first

Dabbled with a couple of MUDs back in 1990.
Played a bit of Diablo on battle net and red alert matches online later on.

First major online gaming experience was Meridian 59. Then ultima online, Everquest and Everquest 2 after which I quit playing mmos.

Definitely Neopets. Oh, I miss it a lot...

TF2 forever <3

Never really was an online gamer, but I gueeeeeess... The Endless Forest, maybe?

Diablo

It was either Runescape or Dungeon Siege, I was around 9 years old the perfect time to start insulting everyone's mom on the internet.

MechWarrior II va NetMech. After that not much till L4D/L4D2, then finally Eve Online.