Ragnarok Online as #1, totally.

#2 would be Dream of Mirror Online. If you want to get anywhere you have to be in a party, since there's an party system you don't have to go anywhere to be put into a party - And when in a party, usually you just socialize while killing mobs. Awareness of the situation is needed but you don't have to be attacking all the time unless you're in a bad group.
Only the Healer and Tank should be aware of when not to talk.
Been in plenty of parties and gotten multiple characters over level 40, the fun comes within' socializing with randoms in your party whilst killing.