Info so far

Here's a summary of the non-multiplayer stuff.

Halo 4 is set in 2557 - four years, seven months and ten days since the FUD was split into two and the finale of the events of Halo 3.
True native 720p with FXAA
New HUD, features subtle paralla movement during athetic actions and additional visual cues indicating that you are actually wearing a helmet.
Chief, Cortana and other characters animated with the assistance of motion capture.
Cortana impending rampancy will be a critical theme as will be exploring Master Chief as a person.
Cortana has chosen a new visual identity whilst the Chief has been sleeping.
The Covenant, at least Elites and Grunts, return but are not the primary enemy.
The FUD eventually crash lands on Requiem, a planet enclosed in a massive Dyson Shell.
A new faction from Reqium is introduced. Like the Covenant they will have unique and different enemy types, weapons and equipment. "If anything, they're kind of elevated in terms of their intelligence and complexity relative to the Covenant."
Huge, alive environments - a piece of concept art depicts a floating air squid in a jungle setting.
The skybox is filled with massive pillars reaching down from above and the surrounding view is painted by the inside of the Dyson Shell.
Game is split between Campaign and Infinity - the new term of the entire multiplayer experience seperate from the Camapign.
Multiplier directly and in-directly ties into the Campaign.
Multiplayer features Spartan IV's - adult volenteers taken from the the best of special ops soliders, equippe with a new version of the Mjolnir armour (lightweight variation) and deployed onboard the UNSC Infinity.
The UNSC Infinity is the largest ship the UNSC has ever created. Over three kilmetres long, it was designed with cutting edge technology and features some additional technological enhancements provided by the study of Forerunner technology - including faster and more accurate slipspace travel.
The UNSC is deployed on a top scret mission into deep space but will cross paths with the Master Chief during the campaign.
The Spartan IV's onboard train in the Infinity's "combat deck" (think holodeck or Danger room). The deck and simulate any known environment and plays host the the multiplayer games players are familar with.
Firefight is absent and it is stated that there are no plans for it to return.
New Co-Op mode called Spartan Ops for up to four players in online Campaign-esque missions.
Spartan OPs introduces new movies sequences and missions on a weekly basis which tells the story of the UNSC Infinity's mission and battles the new Spartan IV's face.
Spartan Op missions are objective based and feature new content, events and locations each week. Spartan Ops missions also reward Spartan Points and feature selectable difficulty levels like Campaign.
Spartan Ops missions are not DLC, they are included in the overall Halo 4 package but it is unclear if the content is available on the disc or must be downloaded separately.
Weapons in the overal sandbox include Assault Rifle, Battle Rifle, DMR, Assault Carbine, Covenant Carbine, Shotgun, Rocket Launcher, Sniper Rifle, Magnum and Plasma Pistol. There are numerous unrevealed, new weapons.

And Multiplayer details summary.

Loadouts are composed of a primary and secondary weapon, a grenade type, armour ability and modifications. It is unclear how the modification system works or what things it modifies or how.
Returning Armour Abilities include Hologram, Jet-Pack and Camo. A new ability to see through walls was shown and Sprint is now a baseline ability all players will have access to at all times.
FFA Variant, Regicide. Lead slayer is "King" - each of the King;s kills raises his "bounty". The bounty is claimed by whomever kills the King.
In Team Slayer (not confirmed for other gametypes), players can respawn instantly after death if they choose. Additionally, power weapons are introduced into a game on a random timer and appear at random drop points on the map.
Medals are turning including new medals for "revenge kills" and for causing a distraction.

Videos of interest

Sound track preview
Halo 4 first look
The team




Thought it was nice to make the Halo 4 thread, now there's plenty of information coming in. This is the real deal for really forwarding the story and fiction with the Halo universe. To those who enjoy this series, Halo 4 will be a evolotion in the series and will be doing justice with its rich story that has been developed over the years through the novels and other media (I would reccomend the Forerunner triology by Greg Bear alone if you enjoy reading or love sci fi), Halo 4 has an amazing team behind it and will deliver the goods (Bungie's writing hasn't been their best trait from the previous entries, allthough Halo 1, ODST were exception to the rules outside of Microsoft's writing team input). Might as well see if there's fellow Halo fans looking forward to this.