I mentioned it briefly in Reclaimer Radio, but I think one way to implement Spartan Abilities without making them too Crysis or convoluted would be that, much like all the other functions your Spartan can universally perform across the franchise, "Spartan Ability" refers to a simple, almost binary mechanic whose diversity stems from the player's intuition. That is, it's a simple "push" or "pull," much like the Thruster Pack, with more advanced capabilities on an XYZ axis. Assuming every action from firing to Sprinting is a toggle and not a hold, analog functionality notwithstanding, let's pretend that this is a magical world where everyone's cool with Halo and Spartan Ability works in tandem with Sprint. For brevity's sake, I'm calling Spartan Ability "Revamp" for this small megapost. It's short for Reactive Entry Variant Augment-Mitigator Pulse or some horseshit.
The Revamp assumes that this is also a more momentum-focused Halo metagame, where combat is highly dependent on players being constantly on the move, regardless of the direction. Hitting the old AA button will cause the Revamp to move you in a Thruster-like juke, dependent on two factors: the analog sticks. The left analog stick allows you to control the XY orientation of the boost, while if you're airborne, the right analog stick sends you across the Z-axis in the direction you're facing, like an extremely low-fidelity sword-fly. So while in ordinary ground-based engagements where you're targeting grounded infantry, it'll act similarly to how the Thruster did. However, combining the Revamp with jumping, falling, etc. you can use that third axis of motion for a variety of purposes, ranging from a double-jump to a juke to just prolonging your airtime - or reducing it. This is where weird stuff like the ground-pound comes in.
Instead of bringing back Halo 2's momentum-based melee system, the Revamp comes with a variation of it, where a vanilla Revamp won't cause any damage, but performing a melee attack at the end of your boost adds a binary (as in, not affected by additional momentum or speed, it's just a simple "does it cause damage or does it not") punchy shockwave effect to it. This shockwave doesn't have EMP purposes or anything ridiculous - it's not even that powerful - the main place the Revamp melee comes in is during team play. Revamp-smashing produces considerable knockback (similar to, say, a Concussion Rifle's bolt) with next to no damage; it mainly produces the spark-flying spectacle we saw in the trailer. It's not meant to damage or outright kill players, it's meant to kill their momentum. For example, if you have a teammate sniping from a distance trying to pick out enemy Spartans in a firefight but don't want to risk shooting your teammates, a ground-pound would scatter everyone and heavily screw with the flow of the gunplay, allowing your sniper to pick them off more easily. As far as one-on-one engagements go, the Revamp-smash is mostly useless if you're facing an armed opponent - you do little to no damage to them, send them further back (out of your immediate melee range) and let them score more shots on you before finishing up with a melee or just a backpedaling volley.
Being such a basic utility would allow it to work without making Sprint a necessity in the sandbox, but at the same time, it also provides certain possibilities by combining them - all sorts of weird map control maneuvers, jukes, momentum-cancels, vaulting leaps over otherwise impassible obstacles, etc. promoting further variety and simultaneously making Sprint a little more entertaining to encounter in combat. Now, if an inexperienced enemy's losing a firefight and attempts to Sprint out of range, you can Revamp to stay on their trail without sacrificing gunplay as they just did - or you could even combine momentum from Sprint and Revamp to launch yourself at them for a backsmack.
.
