"A new 'party' game ," says Bungie, "where the goal is to collect and capture the most skulls."
"Another 'party' gametype that is sort of like Territories meets with Capture the Flag."
"Three Spartans against three Elites. The Elites are trying to destroy three generators before time runs out while the Spartans are trying to defend."
"It's a vehicle-full frenzy!"
However, "not everything will be available day one," as community director Brian Jarrard explained. "There will be five different playlists active at different points during the public beta... as the beta progresses, more playlists will come online. You'll have Arena stuff, you'll have Free-for-All, you'll have Grab Bag which is a mix of different game types, and you'll have the Invasion and Network Test 1 playlists."
As for how these new modes correlate to the beta's four maps, multiplayer designer Lars Bakken provided a brief breakdown: "You'll see variety on Powerhouse or Sword Base because those are our 'Slayer maps' or our 'party game maps.' We can't say much about Boneyard or Invasion [only playable on Boneyard], and yea, Overlook is specifically for Generator Defense (or 'Network Test 1 Beta' as we call it)."