"Built from the ground-up for cooperative play, Halo 5 features a seamless jump-in-drop-out system. At all points in the game you will be accompanied by your AI companions on either Blue Team or Osiris. These characters, of course, can be replaced with real players at any point during gameplay. Each character has a unique helmet/HUD, weapon loadout, and voice. If you play as Linda from Blue Team, for instance, you will always start with a Sniper Rifle. Throughout the missions the characters will talk with each other. If your character is speaking it will sound as though it’s inside your head rather than over a radio. This sounds obvious, but it became noticeable replaying the same mission as different characters."
"To make Halo 5 a true coop experience, for the first time ever you can be “downed”. When you die, you’ll drop to one knee on the floor and await revival. You have a limited time to be revived before you fully die and have to wait to respawn. To revive, an ally simply needs to stand in proximity of you and hold the use button. He then raises a holopanel, types into it, and blasts you with rays of green light. Magic. If you are killed by a more deadly force like being stuck by a Plasma Grenade you will be instantly killed with no option for revive."
"After getting the run-down, we were shown a brief campaign teaser. It moved so fast it was hard to point anything out. That being said, what my eyes feasted upon was
jaw dropping: massive enemies, space battles, and more. I saw Hunters forming from worms (Lekgolo) on the ground, Banshees flying past a space station, and a flying Forerunner vehicle shooting at a massive covenant station (it almost looked like a mining rig).
The scale was unlike anything we’ve seen in Halo, specifically the giant vehicle scene. There were vehicles flying around, Covenant shooting plasma through the air, and explosions illuminating the landscape. It was hard not to get excited. We watched it twice. I am very certain that the space banshee scene was a playable experience. Halo 5: Space Battles. Colour me hyped. A new enemy type was briefly shown called the Promethean Soldier. It’s a more human-like enemy that moves fast and looks to be a handful to deal with."
"The host of a game must always be either Master Chief or Locke. He can still give orders to direct the team, but nobody else has this ability. When joining a cooperative game you may select any other character to play as. Ultimately character choice has no effect on gameplay except for your initial loadout weapons."
http://www.readyuplive.com/2015/06/my-halo-5-guardians-experience/