So, even though we've talked about how poorly implemented the Forerunner weapons are, we've rarely discussed what would be better. Well, here I am, drunk with nothing better to do on Sunday night, and I'm going to talk about how I think the Forerunner weapons can be improved.

First point of order, most Forerunner weapons would be power weapons.

No, wait, better point of order: Forerunner weapons would not make an appearance in multiplayer. Except for Juggernaut-style playlists. I dunno. The point is that if you're complaining that my suggestions would be 'unbalanced', you're missing the point.

Reload Mechanics

Much of the aesthetic design decisions should reinforce the fact that the Covenant were inspired by found Forerunner tech. So, battery power is the way to go.

And while Forerunner weapons would be more powerful than their (vaguely) counterparts in the Covenant arsenal, they would have less battery power. Gameplay-wise, this prevents them from being too powerful to design encounters around. Canonically, it would be because Forerunner weapons draw power from the user's suit, which gives them a nearly limitless operating life. And when you separate the weapon from the user, all that's left to draw from is a reserve in the weapon. Maybe there's a way to replenish the battery from the Chief's shields a few times before the weapon burns out. That way, you have to finish the encounter or retreat before you can use that Stasis Rifle again.

Nuts and Bolts

To start with, I would give the sticky detonator and the railgun (IE: two of the three exotic weapons in the entire gorram game) to the Forerunner instead of the UNSC. The railgun wouldn't need much of a change mechanically to work as a Forerunner weapon, though the reload animation would be changed to reflect the fact that Forerunner weapons don't use physical ammunition.

The sticky detonator is now the Incinerator, and I've got two different ideas for how it could be implemented. But first, I would like to point out that it's called the Incinerator because it lives up to that name. I'm not talking about some piddly dissolve animation that's used to hide the body. I mean full-on incineration. One instant, you've got an Elite. The next instant, you've got a rapidly expanding cloud of ash and steam and maybe chunks of ceramic from its armor.

The first idea mates the Sticky Detonator with the Target Locator from Reach. You point it at a target and hold down the trigger long enough for the weapon to lock on. Once it's locked on, the function is identical to that of the Sticky Detonator: You're shown a screen of the target and nearby enemies. Release the trigger to vaporize the target and bowl everyone else over with the explosion.

Alternatively, the Sticky Detonator could still launch a munition. When the munition (Misleading name) latches onto an enemy, it envelopes the target in a heavy shield and then detonates a micro-nuclear warhead. Therefore, while it would deal much less damage to bystanders, whatever it hits is destroyed. Ghost? Gone. Wraith? Gone. Phantom? Gone, along with its passengers.

Now for the less powerful weapons.

The Stasis Rifle is a less-lethal police weapon. It immobilizes a target by projecting hard, inflexible shields around them. This protects innocent bystanders from stray gunfire, but leaves enough of the target exposed for a coup de grace.

It's useful for really tough targets like Hunters, but also for facing crowds. If you immobilize one Covenant, two more will break off the attack to free him or provide cover. In addition, if you shoot your allies with it, it gives them overshields.

The Suppressor (For lack of a better name) embodies all the talk about transformation. The shape of the weapon is different depending on what is holding it (You, Elites, Grunts, Sentinels, and whatever else the Forerunner brought to the game) and the projectiles change shape, luminescence, and color depending on what you're shooting at, and whether it's got heavy armor or shields. Visually, it should probably take cues from the plasma rifle.

Along with the Sentinel beam, this would probably be the utility weapon for the Forerunner.

Finally, there would be Halo's version of the Gravity Gun. It's long overdue.
This is a device a little bigger than the Covenant energy sword. In the hands of the Forerunner, it would let Sentinels turn everyday objects into projectiles, and it would replace the Watcher's shield mechanic. Instead of a shield that you have to wait to run out, Watchers or whatever replaces them would generate a singularity that sucks in bullets over a period of five or ten seconds, and then fires the bullets back at you in a shotgun-like burst. (Think District 9)
To counter this, you could throw a grenade at the singularity and then shoot it, or you could switch to a plasma weapon which is diffused but not blocked.

In the player's hands, the Gravity Gun lets you pick up and throw objects. Whoop de do. The real magic is how it modifies your melee. When you melee, it projects an energy blade. When you hold down the melee button with the reticle centered on an enemy, you lunge.
Maximum lunge distance is something like thirty meters.
Yes, ladies and gentlemen, that's right: This thing lets you recreate sword flying from Halo 2.

I guess... there's also a grenade. And a long range sniper rifle? I dunno. I guess the Pulse Grenade and the Binary Rifle could be modified and beefed up.

And goodnight. I shall likely be sober in the morning.