The zone can hold up to 24 people. It's group content, so you're expected to go in with a 6-person group. However, your group doesn't need to start with other groups, or even work together for the most part. So it's like a normal zone which just happens to have a few groups working inside.
The zone itself is not linear, but has many paths. There are also portals, and you can use windwalking and gliding abilities to quickly move around the zone.
There are essentially four classes of mobs inside the zone: regular mobs, lieutenants, captains, and the endboss (a vice-admiral). Regular mobs and lieutenants do not share tags between groups, but the captains and vice-admiral are shared. This pushes the groups to go their separate ways to guarantee they get credit for the regular and lieutenant kills, but also converge to kill captains and the vice-admiral together.
|Vice-Admiral Poharan of the Blackram Marauders|
There are a set of dailies at the start that cover the entire zone. Kill a bunch of regular guys, kill a couple of lieutenants from each section, kill each captain, and kill the vice-admiral.
Everything respawns after a bit, so the zone is essentially continuous in time. It is never "cleared". A captain spawns about every 5 to 10 minutes. The spawn is announced to the zone, and a marker appears on the map. After several captain kills, the vice-admiral spawn is announced. The groups have 5 minutes to get to her area. Then the vice-admiral spawns and everyone kills her together.
This probably sounds relatively simple, but in practice I find it just works. A group goes into the zone and starts working on their dailies. When a captain spawns, the two or three closest groups make their way to it. After the captain is killed, one group will take one exit, and the other group will take a different exit. After a while the vice-admiral spawns and all the groups in the zone will converge on her location. Groups that finish all their dailies zone out, and new groups replace them.
The dailies provide natural direction to determine what the group does. They can't just sit and farm in a lucrative spot, they have to go around the entire zone to find the lieutenants and different regular mobs required. The tagging rules encourage the groups to spread out and not move as a giant zerg. But you still come together for boss kills. Finishing all your dailies gives you a nice stopping point, rather than grinding rares for hours.
I've complained about WoW's blue bar areas before, and I think BnS's raids are a further, better evolution of the general idea. I think they're a good model, especially the clever tagging rules, for producing interesting open-world group content.