1) Having to have multiple accounts to play the game.
Reasons this occurs: low population, leveling ramp = leveling ziggurat.
Worst offenders: Shadowbane
2) VOIP metagaming
Reasons this occurs: when PvP is designed on PvE models.
Worst offenders: WAR
3) Class/Race power imbalances
Reason this occurs: shoddy design, favoritism
Worst offenders: WoW
4) Not listening and/or lying to the players.
Reasons this occurs: power trips, desperation to find a new audience
Worst offender: Probably SWG, but since I missed that little debacle it would be a tie between Vanguard (GU4) and EVE (Apocrypha NPE).
Okay well, I put up with all of them for awhile, but all of them are irritating beyond measure, and some in truth *were* game breakers for me – all but #4 actually. Probably only because if #4 was a game breaker, I wouldn’t be playing any games at all.