Grand Theft Auto IV's multiplayer earns the worst experience hands down. For one, it sucks at putting you in new games. Time and time again have I seen people try to leave a game I was in only to be put right back into that same game with us. They do it again, and they come back. Leave, come back. Leave, come back. Just... come on.
If you're not the person who made the room, all explosives lag - which is especially irritating on the Ballad of Gay Tony DLC due to the explosive sniper rifles and AA12 Frag-round, as well as the upgraded Annihilator and N.O.O.S.E. APC. Makes the explosive part kind of... hard to use.
The excessive amount of other hindering and problematic glitches is also bad. Sometimes the game makes it that NO vehicles spawn, at all. No cars, none of the placed vehicles, nothing. And it can stay that way for a LONG time - my friend and I once had to run from the third island to the airport (on the opposite side of the map entirely) and even then, nothing was spawning. Not to mention, the game often experiences texture glitches - where certain objects and stuff do not spawn or are invisible, from poles to buildings, it happens.
And the worst of them all - game modders. There are so many, and they can do literally everything and anything to themselves and to you. I hate their actions, and all of them irritate me to absolutely no **censor** end. They are generally all cowards and completely asinine in mannerisms. So many of them ruin games when they join - making you unable to leave, control your vehicles, or even do ANYTHING (setting you on fire at random whenever they want or making explosions happen all around you/your vehicle).
I could also put DBZ Ultimate Tenkaichi up there, too. But GTA has so much that ruins it. I mean, one minute you're loving the game, the next you want to kill everybody in the game server (within the confines of the game, of course) and go play something else - like Skyrim or Halo. At least when everything goes well, GTAIV is a great game to play with a party.