I don’t claim to be a Halo expert, but I definitely consider myself an enthusiast. Here are my suggestions that I think would dramatically improve the Halo campaign.
First, I would take out all the foolish power-ups in multiplayer and introduce them into the campaign. Many people may like all the options available in the multiplayer mode, but I for one wish they would bring back a Halo 2 style of gameplay. For instance, introducing some kind of weapon drop in the campaign would be a nice touch for when you run out of ammo.
The Chief, or any Spartan for that matter, are elite super soldiers, but the gameplay doesn’t do a good job of conveying what they’re really capable of. The Master Chief is an incredibly fast, super strong, very agile war machine. He is also a tactical genius. However, the gameplay only offers a limited range of his capabilities. Basically it’s run, jump, shoot. Imagine if you were able to dive, block enemy melees, and perform counter attacks, strip weapons, side step, or use their outstanding close quarter combat skills! Also, Spartans are basically unstoppable if they’re able to work in teams. It would be cool to have like one mission where you worked in a team and could use other Spartans in a SOCOM like manner.
Some players like the old ‘shoot em up method’, just destroy everything between them and their mission. Other players enjoy playing stealthier. Combining aspects from Call of Duty and Splinter Cell would be something to consider. Let the player have more freedom and decide what kind of Spartan they want to be.
Your gear should directly affect your gameplay as well. Before each mission you should be able to choose what gear you want to use. Similar to the multiplayer loadouts, it would be cool to be able to pick what weapons and tactical gear you can use. The amount of gear you can have equipped should be limited, but the more you take should cause you to move more slowly, and the less you take would enable you to move faster. Your armor could dictate how you play as well. This brings me back to my last example. If you are a stealthy player, having recon style armor would allow you to move faster, but would be less resilient. As where a more combat based armor could take more punishment, but also limit your speed and endurance. This storyline is based over 500 years in the future, but it seems that Call of Duty is more technologically advanced. They have holographic sights and are able to call in air strikes etc… I think it would be awesome to see some way advanced gear or even crazy ammunition. Maybe have some kind of mini-nuke bullets or plasma filled shredder rounds. The MJOLNIR armor is way underrated in the game as well. Equipping different types of helmets could have different advantages. For instance, offering a thermal vision with one type or another type could have an uplink to air support allowing you to call in for precise air drops or air strikes. And the rest of your armor could have special perks too. Like in the multiplayer mode, one type of armor could allow faster shied recharge, and another could be more resistant to explosives or EMPs.
In conclusion, I think that adding a wider range of gear selections, introducing tactical options, and allowing more freedom to choose what kind of character your Spartan is could potentially recreate the Halo experience and have endless possibilities to where it would go from there.