Following Halo 4's announcement, O'Connor reported that both Master Chief and Cortana would undergo "radical" changes in appearance for the game, some of them attributed to better graphics and others to story elements. The studio wanted Master Chief's appearance to convey an imposing mass and weight, to show that one of his characteristics is his 800-pound (360 kg) armor. They studied the armor changes that were made for the Spartans in Halo: Reach, which were much bulkier than renditions in previous Halo games. Character and concept artists began redesigning the Master Chief by creating sketches; these sketches would be rendered into 3D models so the team could analyse the design from every possible angle. The team would then return to creating sketches to make adjustments, and repeat the process until the main structure for the Master Chief was created. The team then worked on the finer details of his appearance.

During the concepting process of Halo 4, O'Connor decided it would be best for the franchise to explore the Forerunner fiction of the Halo universe, which had remained largely a mystery before 343 Industries' involvement in the franchise. This ultimately led to the creation of a new race of enemy, the Prometheans, warriors of the Forerunner empire. Given that the Forerunners themselves had never been featured in previous Halo games, the design process for the appearance of the Prometheans was long and tedious. The art team produced a large number of sketches, which were presented to other member's of the studio to get feedback and reactions. Many variations of different character models were concepted before the team decided on a final design. The main goal when designing their appearance was to make them resonate with the player, and evoke the image of the Forerunner architecture and language that had been portrayed in previous Halo media. Upon death, the Promethean Knight dissolves from the point where it was last shot; this visual effect also occurs when certain enemies are killed by Promethean weapons. From a gameplay standpoint the design for the Prometheans also needed to fit in well with the sandbox so they would be suitable enemies to fight. A goal when designing their behaviour was to make them highly adaptive from a tactical standpoint. For example, the Promethean Knight can phase in and out of space, allowing it to retreat or charge the player at any given moment; this changes the way that a player engages in a combat encounter.

Holmes explained that one of the goals for Halo 4's campaign was to incorporate more human elements into the story. To accomplish this the team wrote a B story that explored Master Chief's relationship with his AI partner, Cortana, who would break down into a dementia like state. The development team realized that Halo 4's narrative could be dense and hard to approach, making it inaccessible for new players. They found that implementing such a storyline into an action game to be extremely challenging and considered dropping it during development. Holmes was adamant about including it; he took inspiration from his mother's battle with dementia, which she was diagnosed with near the start of the game's development. This led Holmes to want to capture the emotion and tell "a perfect story".

The senior art director for Halo 4 is Kenneth Scott; he described the visual style of Halo 4 as being more ingrained in the expanded universe fiction, and more "mature" than before. With the game's increased focus on the Forerunners, the artists invested heavily into the look and feel of Forerunner technology. The game also features more diversity in Forerunner structures, including fully active Forerunner technology as opposed to the mostly inert and abandoned structures seen in the earlier games. The majority of the game is lit statically using lightmaps; this allowed the art team to achieve realistic lighting effects with full global illumination andambient occlusion. Image-based lighting is also used to ground scenes and make everything fit together better.

The cooperative Spartan Ops mode originally began as a Firefight-type mode, similar to that featured in Halo: Reach, but was composed of different objective-oriented mission types. Over the course of development, changes were made to Spartan Ops to include a narrative that would tie Halo 4's multiplayer together. The missions were designed primarily for four player co-op. The Spartan Ops development team worked with the narrative team to use ideas and storylines to shape the mode such that the cinematics would tie in with the missions.

Glasgow based animation studio, Axis Animation, assisted 343 Industries on the creation of CGI cinematics for the Spartan Ops game mode. Axis have produced animations for numerous video games, including the award-winning announcement trailer for Dead Island. To make each Spartan Ops episode as engaging as possible the team at Axis shot and edited episodes in live action using performance capture. The team then used the reference cameras at the live action shoot to create a performance edit, before shooting with CG cameras to provide more coverage of all scenes and a greater selection of shots for the editorial team. The shading team at Axis made use of the 3D animationpackage, Houdini, to procedurally generate the environment in the cinematics. Axis worked with Glasgow-based audio post production company Savalas on sound design and the final mix for the Spartan Ops cinematics. Facial motion capture was also utilized to take the movements and facial expressions from actors and apply them to the in-game cinematics for both Spartan Ops and campaign. Performance capture for both campaign and Spartan Ops cutscenes was directed and recorded at Giant Studios. Axis worked in conjunction with Giant Studios and Cubic Motion to develop a special facial motion capture solution that would retain facial expressions from the actors when creating the animation.

Visual effects house The Sequence Group, who had previously developed animation for Halo: Combat Evolved Anniversary's terminals, returned to create additional animation for Halo 4. The Terminals feature a painterly artistic style, which Sequence president Ian Kirby felt appealed to gamers familiar with the style of concept art. In addition to creating the visuals for the Halo 4 terminals, their work appeared in one of the game's main cinematics. To save time and expense using traditional motion capture methods to animate the 3D characters, The Sequence Group used twin Microsoft Kinect infrared sensors to create a home-made solution.

The game utilizes much of the "sandbox" that has been featured across all six prior Halo games and other media, in addition to introducing new characters, weapons, vehicles, and other elements. The game engine used is a heavily modified version of the engine established by Bungie. Unlike previous games in the Halo series, Halo 4 runs natively in 720p resolution. The game itself comes on two discs and requires 4GB of available storage space either on a 8GB USB flash drive or Xbox 360 hard drive to play the multiplayer component. Disc two is used to install the multiplayer content and disc one is used for launching the game. Due to rendering issues and significant engine changes, Theater support for Halo 4's campaign and Spartan Ops was not featured in the game on launch; however 343 Industries expressed that this feature may be implemented in the future.

As with previous Halo titles, 343 Industries provides a statistic tracking service for players of Halo 4. Player data such as game history, character progression, and various statistics can be accessed in game or via the Halo Waypoint website. The web services team at 343 Industries utilized the Windows Azure Service Bus messaging infrastructure to relay data from the Xbox Live network to back-end databases, where player data and information is stored. Halo 4 player data can also be accessed via theXbox SmartGlass application.