Going to discern as much as a can from leaked screenshot's and the E3 trailer.
The new enemy are called the "Promethean", which appear to be a non-organic species, with three known classes:
Crawler (The dog/ticker like creature from the trailer)
Watcher (The flying robot construct that can catch grenades from the trailer)
Knight (The badass robot that can teleport and whatnot from the trailer)
The vehicles known to be returning so far are:
Warthog
Mongoose
Ghost
Banshees
Spirit (Maybe)
Elephant (Shown in the trailer but not sure if you can drive it)
Unknown Dropship (Shown in spartan ops video, looks like a crate)
The weapons returning so far are:
Assault Rifle
Battle Rifle
Designated Marksman Rifle
Magnum
Rocket Launcher
Sniper Rifle
Spartan Laser
Plasma Pistol
Needler
Energy Sword
Carbine
Human Turret (Can rip off and use in combat)
And the new weapons known so far:
Sticky Detonator (Rocket Pistol shown in trailer)
Storm Rifle (Functions like the plasma repeater as seen in spartan ops/mp gameplay)
Scattershot (Appears to be a form of shotgun)
Light Rifle (From the gameplay looks like a single burst rifle)
Armour Abilities:
Promethean Vision (See through walls at the expense of distorting your vision)
Regeneration Field (May work like the healing field equipment in Halo: 3)
Hologram (May work like it did in reach, creating a moving hologram of yourself)
Hard light shield (Shown in the E3 trailer and the multiplayer trailer I will post)
Active Camouflage (Self explanatory)
Thruster Pack (Short range jetpack?)
AutoSentry (An automated turret that can defend strategic points such as king of the hill objectives)
Specialisations?:
Firepower (Allows the use of two primary weapons (In Loadouts))
Resupply (May restore your ammo?)
Grenadier (Grenade launcher?)
Awareness (May bolster your radar into a super radar?)
Shielding (Gives you extra shields?)
AA efficiency (Armour Abilities last longer?)
Extra Info:
Cortana is going to become a rampant bitch and make your life a pain
Infinity crash lands on "Requiem"
"Promethean Vision" appears to be a form of thermal vision.
The voice at the end is probably "The Didacts" as the voice is accompanied by his symbol.
There is a high possibility the enemies are going to be "forerunner" due to the fact that "Promethean's" were a type of warrior class in the forerunners society, it's also possible that they were changed over time and whatnot.
The ball shown contained the Didacts symbol, but it could also be anti-Didact as it was turned upside down (Inverted cross).
Sources:
http://halo.xbox.com/en-us/Universe...8a8-d6fd-4c01-9f46-d9a97fcd9cc1#imageNumber=1
https://www.youtube.com/watch?feature=player_embedded&v=FPp1sXgQB58
http://www.youtube.com/watch?feature=player_embedded&v=hbZ3FlcNGpU#