Tl;dr
WvWvW PvP Theres 2 flavors of PvP, one is the Arena style combat that GW1 is currently known for, the competitive style. The second kind is World vs World vs World where 3 servers are pit against each other every 2 weeks to battle it out across 4 persistent maps filled with 2,000 people that involve capture points, resource gathering, castle sieging, etc.
Long Story copypasted
World vs World PvP
WvW consists of three servers pit against each other in four gigantic maps where you fight over keeps, towers, and resource points over a two week period. WvW can hold 2,000 people, 500 per map, and 666 from each server. Theyve said theyre trying to increase this number where possible. Now that the basics are out of the way, well talk about specifics.
After each two week fight, servers will be ranked against all other servers and pit against servers of equal challenge. This all takes a matter of minutes and you can then jump right back into a new fight once the new servers are chosen.
Each server has a home map called Borderlands, and then the neutral center map is called The Eternal Battleground and has its own unique features and a massive central keep. Every map has keeps, towers, and resource points to take over as well, but more on that later.
Capturing keeps, towers, resource points, and other objectives will earn your server War Score and its periodically tallied throughout the two week fight and determines the overall winner.
Keeps Keeps are extremely large structures that can be fought over, they have massive walls and doors that can be broken down to gain entry. Every keep has defensive tools to help you keep your enemies at bay though, tools such as pots of oil, cannons, and mortars. Keeps also have NPCs that protect it for whoever currently owns it and can be upgraded (more on that later). Once you get past the gates, the NPCs and enemy players guarding a keep, youll then face off against the lord who defends the keep. Defeating him will grant ownership to your server and possibly even your guild (more on that later).
Towers Towers are medium sized structures that have less NPCs and smaller walls & doors than a Keep, but are still a challenge meant for smaller groups of players.
Resource Camps Resource Camps are extremely important because theyre how you gain supply. Supply is essentially a resource that allows you and your server to repair walls that have been destroyed, purchase keep upgrades, build siege weapons, and upgrade NPCs at keeps. Each Resource Camp has a small group of NPCs guarding it, but no walls or doors to speak of. If your server owns a Resource Camp, caravans will periodically be sent out to resupply nearby allied towers and keeps. Each objective has its own supply depot, but only if its available at that depot. If not, youll need to escort a caravan to a nearby depot or obtain some from a Resource camp.
The caravans and such are like Dynamic Events, theyre shown on the tracker to anyone nearby, for you they might say Escort the caravan to the keep., where as any enemies nearby would see Stop the caravan from reaching the enemy keep. This facilitates PvP in many areas of the map rather than people standing in one spot at a keep or tower since supply is an extremely important part of WvW play.
Upgrades Each location type can be upgraded in some way, from structural upgrades of a keep or tower, to upgrading the strength of your allied NPCs.
Structural upgrades strengthen the defenses of a keep, making them much harder for enemies to destroy. You pay the gold upgrade cost immediately, and then worker NPCs will gather the required supply from the keeps depot as they build the upgrade. Only workers are able to spend supply on a structural upgrade, and the upgrade only completes once enough supply has been spent to build it.
Personnel upgrades affect the NPCs at your objective, allowing you to hire more guards or raise the level of any guards in the area. You pay the supply and gold cost up front, and then you must wait for a period of time before the upgrade is completed.
Siege Weapons Siege Weapons come in 5 different flavors that anyone can build as long as they have a blueprint and some supply. To purchase a blueprint you just have to find a allied Siegemaster NPC and then you can double-click the blueprint and place it where you want. Once youve done that the blueprint is consumed and requires supply to be built, however it takes more than just one supply to build so anyone on your server who has supply on them can add it to your siege weapon and speed up the construction. The same thing applies to the defensive siege weapons on keeps and towers, you dont need a blueprint for those, however you do need supply to build those as well. Heres a list of the Siege Weapons:
Trebuchets Earlier I described how keeps and towers were extremely well protectedhow could one ever hope to break through such formidable defenses? Might I suggest launching huge, flaming balls of destruction from your very own trebuchet? This long-range death dealer is a high-value target that often attracts enemy counterattacks, so make sure to protect your trebuchet!
Arrow Carts These deadly projectile launchers can blanket a small area with arrows, easily cutting down flesh-and-blood enemies, but they are largely ineffective against walls and gates.
Catapults A good choice for taking down walls and gates, catapults attack a larger area than arrow carts, so they can also be very effective in putting the hurt on a tight group of enemies.
Ballistae These siege weapons launch giant bolts that can pierce their target, dealing large amounts of damage to players, gates, and walls alike.
Siege Golems Do you need to bash down a gate? My friend, you need a siege golem. Thats right: in world vs. world you can build your very own asuran golem, a robotic juggernaut that will smash things for youalbeit at a leisurely pace. It takes a lot of power to mobilize something that awesome, so the golems dont move very quickly. They also dont have much in the way of ranged attacks, but once a siege golem gets close enough to start bashing on a door, that door is in trouble.
Orbs of Power The Orbs of Power spawn in each of the three home Borderland maps each time a new battle starts. Every keep contains an Altar of Power in which the Orb must be returned to. Each Orb is guarded by an extremely powerful foe called Keeper of the Orb who resides in a heavily fortified area called Cradle of Power. Once you have the Orb in your possession, you must get it to an Altar of Power within minutes otherwise it returns to the Cradle. If you manage to get the Orb into the Cradle, everyone in the Mists on your server will receive a boost in power.
Objectives & Bonuses As I said above, capturing objectives is how your server gains War Score and ultimately wins the battle through accumulating points. As your server gains more War Score, everyone will be given additional bonuses outside of ones you gain for your character and ways to upgrade the bonuses you already have. Guilds are able to claim locations, such as a keep or tower, and attach bonuses that they have to those areas and to everyone else in the area. Bonuses such as: more health, increase stats, increase how much supply that you can take from a depot in that area. However, a guild can only hold one location at a time, so they must choose wisely.
Getting help from the locals Around the Mists you might encounter groups of races who inhabit the many Mercenary Camps around the map. You can enlist them to help you out with your war effort, though you have to help them first. For instance, you might help a group of ogres protect their camp against constant harpy assaults. In return, your new ogre allies will go rampaging toward the nearest enemy objective or send out patrols to help you hold on to your territory. These factions wont fight for you indefinitely, but they can help turn the tide of battle, so youd be wise to recruit their aid whenever possible!
Getting into the fight at any level Youll be able to jump into WvW right at level 2 with the same character you just created, no need to make a separate character. When you get in youll be at the portal at the entrance to your servers Borderland. Your stats will automatically be adjusted to appropriate stats for a level 80 character if youre under level 80 so this allows everyone to be on somewhat of an even footing. Granted that level 80 character is going to have a lot more skills, Traits, and experience, you wont be instantly killed by the level 80, but they will have a clear advantage. Though this doesnt mean youre worthless, you just cant expect to go up against a level 80 at level 2 and win. Theyve mentioned that one-vs-one fights arent too common so it shouldnt be all that much of an issue. While in WvW players and mobs will give you XP and loot that is appropriate to your level when killed so you can level all the way to 80 while in WvW. When you jump out of WvW you take everything youve gained with you back into the PvE world.