It seems that at least it will bring 100v100v100
Arena Nets Blog does a very good job in describing it in detail.
Here are the highlights for me:
we needed to make some absolutely gigantic maps—four of them.
Each objective on a map is worth points for the team that captures it. We periodically tally the point total for each server and add that total to their War Score, which accumulates over the length of a persistent two-week battle.
If you don’t quite have the numbers to go after a keep, there are quite a few smaller towers placed around the countryside. These more modest fortificatihttp://www.blogger.com/img/blank.gifons are perfect for smaller groups to assault and defend. But just like the larger keeps, towers have their own sets of defenses you’ll have to deal with, including a compliment of NPC guards and destroyable gates and walls.
We wanted to make WvW fun and easy to get into, so there’s no level grinding required—you can just hop into the battle using your normal PvE character, regardless of what level you are.
you continue to gain experience and new items while playing in the Mists. Players you kill will drop loot for you just like slain monsters in PvE.
A deluge of information is linked here.