Well it appears that the first details on Halo 4 have reached the Internet thanks to a member of the Bungie Forums.
Of course there is no proof to say just how real these details are so it’s your personal choice if you believe them or not, just a quick warning if it is true then it does contain spoilers.
Halo 4 returns players to the story of the Master Chief and
Cortana in the events that follow the conclusion of Halo 3. Players will
experience an all new story and introduce a new roster of enemies and
weapons to the Halo experience. Set against the top secret Forerunner
planetoid known to ONI as Sigma 7, players will encounter a dark new foe
and unravel more of the mysteries behind the forerunners and the Office
of Naval Intelligence.
At the heart of Halo 4 is a stronger focus than ever before
behind story telling and player choice. Players will be offered an
unprecedented level of customization and a narrative experience never
before seen in a first person shooter. On a technical level Halo 4
pushes the boundaries of the action genre by incorporating larger
battlefields than ever before and players will experience conflicts that
seamlessly span land, sea and space.
Halo 4 will expand the series trademark arsenal of weapons and
vehicles beyond any other title so far. Players can expect fan favorites
to return along with new additions. Halo 4 will also feature the
revolutionary new Arsenal Improvisation Mechanics that allow for
menu-free, creative customization of weapons and vehicles in the heat of
combat. Players will take their fight to a new level by dynamically
tailoring their weapons and vehicles to suit any situations or enemies.
At the moment it seems 343 are focusing on the new and improved
story and weapons system (of which the new AIM mechanic is only
mysteriously alluded to) but there was some video shown that fills in
some of the gaps. Halo 4 is set on a Forerunner planet that has an inner
and outer surface that provides two distinct styles. The outside is
very industrial and features a wide range of hostile Forerunner tech and
AI. The video showed space combat here. The inside of the planetoid is
hollow and is sectioned off in to many tiers/bands (almost resembling
Halo rings) that feature a myriad of natural environments not only
resembling earths but many other alien terrains. The video featured
combat across a multitude of environments from space to mountains,
plains and oceans. Presumably, ONI had been top secretly researching the
planet for some. There are UNSC forces on the planet but they look
really degraded and disorganized and it was implied that they may be
divided into factions and warring with each other. At one point we see a
heavily modified warthog that has had the wheels replaced two kind of
anti gravity devices. At another point the Chief is clearly sprinting
which possibly implies a return of armor abilities. There was no sign of
the Flood or the Covenant but at the very end of the trailer the dark
new threat was hinted at. The video ends with the Chief standing at a
dark cave entrance and from within can be heard some menacing gurgling
and grunting. Cortana says Theyre coming back and theres a LOT more
of them this time, the Master chief then readies a new weapon that
looks like a cross between a rocket launcher and a Needler and it
focuses on his helmet and visor and a number of strange digital effects
ripple across his visor then the videos ends.