The first title in the 3D Grand Theft Auto series to introduce a multiplayer aspect was San Andreas. Quite frankly, it was nothing special. Felt tacked on at best. Things may change when the fourth entry in the series rolls out this April.
According to intel gaming blog Destructoid has received from an "reliable" anonymous source, GTA IV will contain a deeper multiplayer experience than its predecessors, including deathmatch, team play, co-op missions, and ranked multiplayer races. Rumored names for the multiplayer modes include Deal Breaker, Bomb da Base and Hangman's Noose.
Perhaps official details on the multiplayer mode aren't too far off - the newly-launched GTA IV website contains a multiplayer tab that denotes "coming soon."
Rumortoid: Grand Theft Auto IV multiplayer, mini-game details [Destructoid]