Hack and Slash game made by Blizzard. Highly addictive.
Player assumes the role of any one of seven different combat classes: Amazon, Assassin, Necromancer, Barbarian, Paladin, Sorceress or Druid. You distribute stat points and skill points as you level up and complete quests. Eventually when you make it to Hell difficulty the fun begins and you have to play smarter.
The online aspect allows players to move faster through the game.("rushing", "cow levels", "baal runs") So having to do the same quests over and over with new characters is usually not a problem online. Also you can play with real life friends, which is very fun, that is until a rare armor drops and then hell breaks loose.
Dueling others is usually kinda lame as there is always some young punk griefer who's played for years and has godly equipment that his level 15 uses to kill your level 50 in the blink of an eye. Also hardly anyone knows how to enjoy dueling or listens to specific rules(like no potions).
(I recommend at least giving the game a try. It should be very cheap in any local store, or you can order it online.
Javazon_ZapUrAzz defeated NovaNecro_BoneUrAzz easily, but couldn't even touch TeleBarb_AxeUrAzz. Then Hammerdin_ZealUrAzz showed up and owned all three of them.