Initiating a battle is very clunky at least for warriors. You have to double click on an enemy to attack it which is nearly impossible when you have them bunched up. Using a tech like slash means that when you kill the enemy you targeted you stop attacking leading to frantic clicking trying to get the character to attack the next enemy. This coupled with the lag makes the defense quests very difficult not because you are too weak to complete them just that very often you just dont have a chance to. Even with no one else using my DSL connection lag is still a serious problem leading to an inability to get the 30 second medal in the Choco Treasure Hunt quest at level 25 (!!).
Many of the quests even the ones marked as low level are frustrating due to this and the fact that grinding is essentially the only way to beat certain quests unless you are lucky enough to find a party of people. I am not kidding I spent over 3 hours total grinding up to level 15-23 only to find the next quests in the area around Ashaya were to difficult given the many enemies bunched together