It's bloody, it's frantic, and it's incredibly fun.
Blizzard has not been shy about the fact that Diablo III will not be an e-sport like World of Warcraft's arenas and StarCraft II's competitive ladder. The game is first and foremost about venturing into the depths of hell and curb-stomping demons.
That hasn't stopped them from throwing an optional PvP Arena mode into the game as a fun side-option. It also doesn't stop it from being crazy fun.
At BlizzCon 2010, only three classes were enabled for the PvP Arena - the Witch Doctor, Wizard and Barbarian. Blizzard has admitted that it would be all but impossible to balance every potential character build (let alone all 97 billion of them), but apparently the Monk and Demon hunter just weren't ready for prime time yet. We were able to take on comers in matches that ranged from 1v1 duels to 3v3 melees - no word on if larger battles are planned.
The PvP Arena couldn't be simpler: It was a medium-sized square pit with pillars and ditches to obstruct line of sight and movement, where healing items would spawn near the center (grabbing one would heal you and any nearby teammates over time). Both teams started on opposite sides of the ring. The team that died first lost. That's it; go murder some people.
Blizzard has said that they don't want Diablo III's PvP devolving into the crowd-control-fest that dominates WoW's arenas, so you'll rarely lose control of your character (though the Barbarian and Wizard both have stuns, and the Witch Doctor has a limited "fear" ability). Instead, it seemed to me that the fighting was much more about placement and clever use of abilities than anything else.
The Wizard was fragile but easily dominated in the right hands. The new Meteor ability clearly indicated to enemies and allies alike (via a glowing ring on the ground) that death from above was imminent, so that everybody knew to vacate the area - or to try to lure the opposition in to certain death. Controlling lanes and movement was very important, as the Wizard's de facto nuke was a Disintegration ray that got stronger the longer they held it - but while holding it, they couldn't do anything else.
The Barbarian lacked ranged abilities but was a monster in close range, and the addition of the Ancient Spear skill gave him (or her) the ability to do just that. The Barbarian takes a page from Scorpion's book and yanks the opponent over to them with a spear - it needs to be aimed and can be dodged with the right timing, but it was incredibly satisfying to use. If you pull someone in and still have your movement cooldowns available like Heroic Leap, they're almost certainly doomed unless others come to their aid.
I never really got a chance to play much as the Witch Doctor, but I got slaughtered by one who sent flaming/explosive demon dogs howling toward me while cursing the ground beneath me to impair my movement speed, so I can only assume that they're powerful in their own right. Best of all, if you die you can still move around the area as a ghost - and while you can't impact the fight anymore, at least you can move around and see what's going on.
For a silly side game, Diablo III's PvP is shaping up very well. It's brutal (if you're unprepared, you can die in seconds from a good tag-team), it requires excellent teamwork and the skillful use of one's abilities, and it's incredibly entertaining to watch a warrior leap through the air in slow motion through your Time Slow bubble, only to land right in the middle of your Meteor circle.
It's also very pretty. Whatever you may think about Diablo III's rainbows and unicorns, those vibrant spell effects look nice