HaloWaypoint has released the following information about gameplay in Halo 4.
Original link for info here (or you can just read it below…): Halo 4 Gameplay

OVERVIEW

Players can engage Halo 4 through a number of ways. In Campaign, players take the role of the Master Chief, the living legend of the Covenant War, a SPARTAN-II super-soldier wearing heavily modified GEN1 Mjolnir armor. Within War Games and Spartan Ops, players take the role of a highly specialized SPARTAN-IV super-soldier, deployed from UNSC Infinity and utilizing a state-of-the-art Mjolnir GEN2 armor system.

In both roles, players can leverage all of the expected abilities of a Spartan: power, speed, dexterity, and resilience far beyond that of a normal human. The player’s Mjolnir armor can also provide individualized specializations referred to as Armor Abilities, such as Hardlight Shield, Active Camouflage, or Jet Pack. SPARTAN-IVs can integrate additional armor modifications, such as Support Upgrades and Tactical Packages, which apply incremental yet valuable improvements to a Spartan’s combat functionality.

     ARMOR ABILITIES

Much like the GEN1 armor that preceded it, Mjolnir GEN2 Powered Assault Armor offers component modularity, which enables users to add physical hardware to their armor, dramatically modifying their combat faculty and performance. The impressive aspect of this attribute is that Mjolnir’s firmware is capable of detecting and translating non-native technology, including the technologies used by both Covenant and Forerunner infantry units, such as the Hologram or the Hardlight Shield.

     THRUSTER PACK

The M805X Thruster Pack, similar to other EVA-focused thrust modules, is a movement acceleration system that mitigates the user’s need for a fulcrum or pivoting articulation. This ability allows the user to move quickly and aggressively in combat, whether closing the gap between the user and an enemy or finding cover.

     HARDLIGHT SHIELD

The recently recovered Z-90 Hardlight Shield appears to be a photon emitter that can fuse particles of light into a rigid, dissipative barrier. For Spartans who choose to integrate it, the technology functions as a full-size aegis-class, anti-personnel defensive shield.

     PROMETHEAN VISION

The Z-5080 Vision Modification system, colloquially referred to as “Promethean Vision,” is a short-range full-spectrum enhancement package that enables users to detect shapes and movement through solid barriers. Coupled with the VISR 4.0 tech suite, this software is one of the most formidable leveraged by GEN2 armor systems.

     HOLOGRAM

The T-27 Decoy package, referred in shorthand as “Hologram,” is a responsive emulator that generates an extremely realistic holographic copy of the user’s physical form and movement. Once used exclusively by the Covenant, this decoy technology has now been reverse engineered for Mjolnir armor systems, and is used as a ruse in the field to trick enemy infantry and armor into revealing their position, thereby placing them at a disadvantage.

TACTICAL PACKAGES

The technological advancement to Mjolnir GEN2 offers Spartans a seamless integration of armor mods to improve their proficiency during battle. Among these are Tactical Packages: software updates that increase Spartans’ combat readiness and responsiveness when configured within their loadout. While Tactical Packages may appear to be marginal in their overall benefit, the pervasive use of them by combat-experienced Spartans argues otherwise.

     SHIELD PACKAGE

Through a modifying bypass of standard performance regulators, the Shield Package reinforces personal energy-shield emitters, resulting in a substantially higher shield-recharge rate. After taking damage, Spartans will notice their shields recharging at a quicker speed than others who have not opted for this package in their loadout.

     FIREPOWER PACKAGE

By alternating redundant magnetic streams at the rear of a Spartan’s armor, the Firepower Package overrides regulated loadout limitations, allowing users to carry two primary weapons simultaneously. For Spartans who prefer heavier or longer-ranged firepower over close-range versatility and speed, this package is typically considered imperative.

SUPPORT UPGRADES

With the recent proliferation of Mjolnir GEN2 armor comes the leveraging of a variety of armor mods, capable of enhancing a Spartan’s combat performance in the field. Critical to these are Support Upgrades, ad hoc technology-based enhancements to a Spartan’s armor functionality when introduced into their loadout. Support Upgrades focus on augmenting combat resiliency during engagements, specifically over protracted firefights and combat scenarios.

     AMMO UPGRADE

The Ammo Upgrade overrides default Mjolnir safety and capacity protocols allowing Spartans to exceed suggested ammunition loads in the field. This upgrade is highly recommended for close-quarters engagement roles and any encounters that require excessive ammunition expenditures.

     SENSOR UPGRADE

Although it violates general UNSC relay transmission regulations, the Sensor Upgrade increases both the range and sensitivity of the standard motion sensor. As it is most frequently utilized by stealth operatives and infiltration specialists, this upgrade provides heightened locational intel of all nearby enemies.

     AWARENESS UPGRADE

Facilitating relatively minor adjustments in an armor system’s HUD-distributed display mechanics, the Awareness Upgrade integrates the default motion sensor into all known scoped weapon smart-links, both native and exotic. Spartans engaging in long-range combat or sniper operations often rely on this upgrade to provide them with basic motion-sensor data while sighting an enemy from afar.

PLAYER PROGRESSION

Through both War Games and Spartan Ops, personnel can effectively rank up, unlocking items, such as armor kits, components, and skins, for use within their custom loadouts. What’s more, Spartans earn points while ranking up that they can use to purchase items to improve their combat performance and abilities in the field.

ARMOR CUSTOMIZATION

As personnel within the UNSC’s Spartan branch advance in rank, they earn a wide selection of armor sets and individual pieces, which they can mix and match to reflect their personal tastes. In addition, they can outfit their armor with alternate skins to elaborate their field presence and identity. Some of the rarest armor sets and components can only be received upon completion of specific in-game Commendations, Challenges, or other Waypoint goals.

ORDNANCE DROP

During the course of War Games simulations and Spartan Ops, drop pods can deploy ordnance into the field. Once on the ground, these pods are marked on the heads-up displays of all nearby personnel who can then acquire the weapons or power-ups for use against enemies. In some simulated matches within War Games, Spartans can earn and manually call in their own ordnance drops.