You can get on a game of GTA4 and usually you'll have quite a few people. For the amount of time I've played it I've only once came across a game with a person I remember that I haven't invited. I no longer remember the name anymore, but I do remember it was in a race.
However, I don't know many people who own the game(a few, that are rarely on.) My bestfriend won't purchase the game for some retarded reason. He's a fan of shooters and won't get it, no matter how much I tell him how amazing the multiplayer is. I let him start a new game to try it out, yet when he finally gets to drive he does nothing but run over people and say the game doesn't interest him. Gee, I really wonder why when you don't do anything in the game but run over people(sarcasm?)