UPDATE: The armor that John-117 is wearing does not have nanorobotics (or nanites) included in his armor, so he couldn't have updated his armor to make these new changes.
Halo 4 is the next title in the Halo series. We have little information on the game so far, but we have enough to get an idea of the game.
The Teaser
From what we could get from the teaser, we know that Master Cheif and Cortana will still be main characters of the game. Master Chief's armor has taken several changes such as the new chest piece, the upgraded helmet, and the "space diaper". 343 Industries said that there is a reason for this change, but they have not revealed that information yet. From the teaser, we could see that the Forward Unto Dawn is being attacked and fiery explosions are happening in it, but there is no such thing as fire in space, so what could that be? Last, the Dawn is heading towards a planet, so what could be on this planet?
The Planet
There is not much known about the planet, but there is little information. The planet is identified by ONI by Sigma 7 abd it's real name is Requiem. It is in fact forerunner, but not much is known about that. There is a bunch of symbols on it (they could be identified on the Halo 3 Legendary Ending) such as, the seventh column, the marathon symbol, and a bunch of other unidentified symbols. During the Halo 4 Teaser and the Halo 3 Legendary Ending, the planet is shown to be made of technology, but in the Halo 4 Concept Art, the planet is shown as organic and not made of technology.
Enemies and Allies
The enemies and allies of Halo 4 is not identified yet, but there are some inferences. They could be the Precursors, the Forerunners, the Flood, or possibly Humans. To support the Precursor theory, there is something at the end of the Halo 4 Concept Art Trailer that has a similar appearence to the description of a Precursor. To support the Forerunner theory, the book Halo: Primordium states that the Librarian is still alive. In the book, 343 Guilty Spark says,"Some say she is dead, that she died on Earth. But that is demonstrably untrue." Although, there are many terminals in Halo 3 and Halo: Combat Evolved Anniversary proving that she did die, that quote could still be a hint. To support the flood theory, the halo rings do not kill the flood, but all sentient life. So, there could still be flood around the galaxy (presumably on the planet). To support the human thoery there is a leaked sequence from Halo 4 of a human pulling another human wearing a scout helmet from the wall. The human VS human war could be because of the insurrection.
Weapons
The weapons of Halo 4 has almost no information, but we could infer what could be the weapons. The assualt rifle should be back since Master Chief left Installation 04B with an assualt rifle. There is an unidentified rocket pistol in the Halo 4 that could be some sort of flare gun since it is muzzle-loaded. The rocket launcher, sniper rifle, and the magnum should be back because there has been no game without these weapons. The spartan laser should also be back since the last couple of games all had them. Covenant weapons could be back because there is a possibility the UNSC started to study the weapons and use them for themselves. The rest of the weapons could be infered once the enemies or allies are confirmed.
UPDATE: The Battle Rifle, Magnum, DMR, Assualt Rifle, Sniper Rifle, and Covenant Carbine has been confirmed.
Vehicles
The vehicles of Halo 4 also has almost no information, but we could still infer what could be the vehicles. The Warthog should be back since there is no game without it. The mongoose should be back since the last couple of games had them (including a beta version in Halo 2). The pelican, longsword, and frigate will probably be back as undrivable vehicles or 343 Industries might let us have our fun. ;) The rest of the vehicles could also be determined when the enemies and allies are confirmed.
UPDATE: The Warthog has been confirmed.
UPDATE: Location
The location of Halo 4 has limited information. As explained above in the "Planet" section, the planet Master Chief is heading towards is Requiem, so it will be a location. The Forward Unto Dawn is definitively a location, since it is the main location in the teaser. Also, in the concept art, you could see a picture of Installation 07. This could mean that it could be a location in Halo 4.
UPDATE: Music
Halo 4 is the next title in the Halo series. Ever since it was announced, we have been able to grab onto a couple of music tracks that have been leaked... Read more >
UPDATE: New ViDoc: "Making Halo 4: First Look"
The rest of Halo 4 will still remain a mystery until a new trailer, vidoc, or leak comes out, but for now Halo 4 will remain as we know it and so far, it sounds awesome.