I have been thinking that I should restart an old tradition - the battlemat. Years ago we played a lot of games of DnD 3.0 where we all built characters and then landed on a complicated bit of terrain to fight to the death. Because DnD 3.0 is incredibly lethal we often spent eight hours building a character only to die in the first round to a 'save or die' attack or in the second round to an incredibly deadly full attack from a martial character. There were definitely some interesting battles where things went back and forth but by and large death was swift. The funny thing is that I had more fun by far building the characters than playing. I would tweak and tweak and rewrite over and over trying to find the perfect mix of items and feats to be INVINCIBLE and there was a real sense that I could perfect a build but when the actual battle started it became very random. If two people gank you, you lose. Even if you have completely monstrous saving throws you still die when you roll a one on your save.
Of course we didn't play unmodified 3.0. Doing so would have led everybody to be flying, invisible spellcasters and nobody being able to actually do anything useful. We had to ban all kinds of magic items like Daern's Instant Fortress so that characters didn't simply hide in an impenetrable vault waiting for everybody outside to die. The list of banned spells and abilities was really quite extensive and pretty much all based around the idea that 'Fighter With a GreatSword' must be able to find and defeat you. If you do anything that means that FWGS cannot win then it is banned.
DnD 3.0 really isn't meant to be a PvP game. At low level FWGS just one shots anybody and casters generally have spells that guarantee death that work 2/3 of the time. At high level things are a little different of course since wizards presumably retreat to their custom demi plane and scry on their opponents to ascertain their weaknesses before plane shifting back with an army of arch demons at their command. Of course if the fighter with a bow goes first he kills the wizard before the wizard can take an action so it is relatively fair. Basically doing PvP in DnD 3.0 involves huge amounts of creation and calculation and then rolling initiative to see who wins because everybody dies in one attack. This leaves little room for tactics and decision making once the game starts so I don't think it is a particularly good format for PvP.
I think 4th edition is actually a pretty good PvP format though. Character stats are drastically more controlled so nobody is going to get their defenses so high that they are unhittable nor so low that they are unmissable. Permanent invisibility or flying isn't available because the designers really seemed to want a random ogre with a club to be a viable opponent so they designed the character abilities around that. This works well for PvP because it means that FWGS can fight anybody. There are some problems still but they are generally really easy to work around. Daily attack powers are totally absurd in a format where you only expect to do one fight so they probably should be banned. Whether or not daily utilities and item powers are okay is unclear to me. Action points are nutty too since all they do is ensure that the first round is an utter bloodbath. You probably need some kind of rule to prevent people just sitting in a corner using Stealth waiting for everybody else to die too I expect. That is all that should be necessary to keep the game interesting I would think. The game still works with action points and daily powers allowed but it would be ridiculously fast and deadly and it seems quite possible that the person with the lowest initiative simply doesn't get to take a turn at all - hardly the ideal result. The end result is still going to be fairly random I would think since attacks will miss half the time and people will gang up but overall it should be a fun time.
What I wonder is what sort of character people would bring. Leaders seem exceptionally powerful because they get to heal themselves so much - that might end up being a real balance problem. If other classes were allowed to multiclass into leader types and use their daily heal ability it would be okay though as the advantage would be mitigated. It is possible I suppose that leaders are so bad at killing that they *need* that massive hp advantage to be playable at all. Hard to say. Defenders look to be fairly strong in many cases since they have massive hp and defenses so they are a pretty hard target. Their defender type abilities are generally going to be bad but just being super tough is a big plus.
The last thing I would think about is the victory condition. It could be a simple last man standing resolution or I could go with a points system. I was thinking about rating people on three scales - damage/healing done, death order and total kills. Rate the players in reverse order and assign them points equal to their ranking - highest total points wins. This rewards a combination of survival, sniping people off and just doing a lot of damage which hopefully gives a good spectrum of rewards.