Top 12 Biggest Changes
1. Protheans: For roughly half of the campaign you will fight Protheans instead of the covenant. While Promethean crawlers and sentinels are relatively easy to kill, the Prothean knights present the largest challenge of any Halo 4 infantry. Not only do knights have much higher shield capacities than Elites, you usually do not have access to a plasma pistol when fighting them, so they must be killed with pure damage. Therefore, you must change your play style and loadout when fighting Protheans.
2. Bigger heads: All of the covenant in Halo 4 have much larger heads than their Halo Reach equivalents. This makes getting headshots even easier.
3. Reduced covenant army: There are no more brutes, skirmishers, or buggers fighting for the covenant in Halo 4. That leaves only elites, grunts, and jackals, which makes fighting the covenant easier.
4. Prothean weapons: An entire new set of weapons accompany the new Prothean infantry. Most of these weapons have a very similar UNSC counterpart, so they do not drastically change your play style. Rather, they can replace your starting weapons once they run low.
5. Regenerative health: Just like in Halo 17 wsm ammo 3, your health once again regenerates in Halo 4. This means that you no longer need to keep track of health kits, and you are safe to take a small amount of damage after losing your shields.
6. Lower plasma energy: Almost all of the plasma weapons in Halo 4 use much more energy than their Halo Reach equivalents. The plasma pistol is one of the weapons most affected by this change; both single and overcharged shots consume much more energy. Conserve energy by charging the plasma pistol as little as possible before shooting. Even if you do this, you will need to swap for a fresh plasma pistol more often in Halo 4 than in Halo Reach.
7. Sprint: Sprint is no longer considered an armor ability in Halo 4; you can always sprint by pressing in with the right joystick regardless of what armor ability you have. This allows you to utilize the other armor abilities at your disposal without reducing your mobility.
8. New Armor Abilities: Although a few of the armor abilities from Halo Reach made their way into the campaign, most of the armor abilities are new. Some of my favorites are Promethean vision and autosentry.
9. More ammo: There are many more ammo crates scattered throughout the Halo 4 campaign, enough you should never run out of headshot weapon ammo. Although you will not always get to use your favorite headshot weapon, you will always have access to at least one of them, even if you miss a lot.
10. Stronger Vehicles: Both the covenant and UNSC vehicles in Halo 4 are far superior to their Halo Reach counterparts. The Wraith in particular is much more dangerous because an elite always operates the plasma turret and its plasma ball is much more powerful and accurate. In general, you should still stun covenant vehicles with a plasma pistol to jack or destroy them.
11. No scoring: There is no longer a way to turn on scoring in the campaign menu, so there is no convenient number on your HUD every time you kill an enemy. Therefore, you need to be a bit more observant. This affected me a lot when I began to play, but after a mission or two, I barely noticed the difference. When you use Promethean vision, the challenge is completely removed because enemies you kill instantly change from red to blue.
12. Less cover: I feel that there is slightly less cover in the majority of the Halo 4 campaign than in Halo Reach. The difference is not drastic, but I do find myself in situations with no good cover more often
No matter what the situation, you should carry one headshot weapons with you at all times. This allows you to instantly kill most of the infantry in the game, and it will also help you when fighting watchers. However, you will need to vary your secondary weapon depending on which enemies you are fighting. When fighting covenant, you should always use a plasma pistol as your secondary weapon to remove elites’ shields and stun vehicles (just like in Halo Reach). This tactic also works to remove the shields of Promethean knights, but because only the covenant use plasma pistols, you often do not have access to a plasma pistol when fighting Prometheans. Instead, you will need to use a Promethean weapon that packs as much damage as possible to kill the knights, such as the incinerator cannon, binary rifle, or suppressor. If available, you can also use the rail gun, SAW, or needler.
Grunts: Headshots are by far the easiest way to kill grunts. Unlike in Halo Reach, there are no more grunt ultras, so you can kill all of the grunts with a single headshot.
Jackals: When a jackal is not hiding behind its shield, simply kill it with a headshot. Otherwise, shoot it once in the hand, causing it to drop its shield and providing you with an easy headshot.
Elites: Overcharge your plasma pistol and fire it at an elite to remove its shields. Then swap to your headshot weapon and finish it off with a headshot.